For those caught in one of the four explosions that ripped through London's subway trains and a double-decker bus, one word captured the terror.
"It was chaos," said Gary Lewis, 32, who was evacuated from a subway train at King's Cross station (search). "The one haunting image was someone whose face was totally black and pouring with blood."
A subway passenger said train cars filled with smoke and there were "loads of people screaming." He said, "You couldn't really breathe and you couldn't see what was happening."
Joanna Myerson was in the tube during the explosion. She talked to FOX News about the horror she witnessed.
"Everybody was screaming, we were all panicking. We realized we were breathing in a lot of smoke and we were actually one car away from where the explosion was.
"The door were locked shut and there was nothing we could do but the smoke was just pouring in.
"If I had been in a different carriage just a few inches over to the right I could have had a lot worse fate.
"Apart from the initial flash, the worst thing was walking through the tunnel past the scene and everyone saying 'ignore what you see'."
Gemma Signes, 32, was traveling on the Picadilly Line when an explosion ripped through the train as it left Kings Cross for Russell Square.
"I thought I’d heard an explosion, a loud bang, but no one knew what was happening. We didn’t hear any message from the driver," she said. Ms Signes was on her way to work in Tavistock Square, where a bus later exploded.
"It was pitch black, you couldn’t see anything, and everyone was screaming and panicking. No one knew what to do. There was smoke everywhere - I could hardly breathe. But someone managed to get the doors open because people started pushing out into the tunnel."
"I’ve been watching the TV since I arrived at work and now I’ve realized how many people died I just thank God I’m alive. I was very lucky. It’s terrifying."
Jacqui Head was on the tube at Kings Cross station. "Suddenly there was a massive bang, the train jolted. There was immediately smoke everywhere and it was hot and everybody panicked.
"People started screaming and crying.
"It was very scary while we were stuck on the train. Very silent and we were thinking we were not going to get out.
"People thought they were just going to suffocate. "
Tas Frangoullides went from one chaotic scene to another because he went from Kings Cross station to Tavistock Square. "The train didn't get very far out of the station when there was an explosion.
"Loads of glass showered down over everyone, the glass in the doors in between all the carriages shattered.
"There was a lot of smoke and a lot of dust, there were some areas of panic, I could hear screams. People were trying to work out what happened.
"A lot of people were covered in blood.
"I started walking towards Russell Square then I saw the bus. Police were running from the scene and waving people away.
"I had to walk to work because I had to try and do something normal, it was all so chaotic.
"It wasn't till I got to work that I realized I had a cut on my head and my clothes were covered in dust.
Fiona Trueman was also at the Kings Cross station. "It was about three minutes after we left King's Cross, when there was a massive bang and there was smoke and glass everywhere - I was standing near a window, and I've still got some in my hair.
"The lights went out, and with the smoke, we couldn't breathe, and we sort of cushioned each other during the impact because the compartment was so full.
"It felt like a dream, it was surreal. "
Delme Jenkins saw the disquieting scene of passengers fleeing the Kings Cross station. "I was coming into work on the bus and I saw a woman who looked as if she'd been crying with mascara running down her face which I thought was a bit strange.
"Then I saw people wiping black dust off their faces and I knew something strange had happened.
"It is shocking, there is a very strange atmosphere around. There is no traffic, people look lost."
Loyita Worley was a witness of the blast at the Aldgate station (search). She told FOX News that people were frantic following the blast.
"People were trying to open doors but they were all sealed up. We couldn't contact anyone because we couldn't use cell phones underground. So, it took about 20 minutes."
"I saw lots of people coming out covered in blood and soot. Black smoke was coming from the station. I saw several people laid out on sheets," office worker Kibir Chibber, 24, said at the Aldgate subway station.
One witness told Sky the explosion was at the back of a tube carriage.
"There was a big hole in the carriage. There were people lying everywhere covered in blood," he said. People were screaming. We could not get out. The explosion was at the back of the carriage."
He said people managed to walk through the carriages to get out, but there were "bodies lying everywhere."
Mustafa Kurtuldu, 24, from Hackney, said: "The train seemed to almost lift up off the rails. It sounded like an impact. It went white and there were flames outside the train, but they died down quickly."
"I was in the next carriage from where the actual thing happened.
"The train almost like lifted up. After about like 10 minutes some guys came, I think they must have been London underground guys, and they were walking along the track.
"The explosion happened at about five to nine and by the time we got out it was about half past nine."
Aldgate passenger Sarah Reid said: "I was on the train and there was a sudden jolt forward. There was a really hard banging from the carriage next door to us after the explosion - that's where it happened."
Describing events moments before the explosion, she said: "There was a fire beside me. I saw flames outside on the window of my carriage."
She said tearfully that as she was led away down the tracks, "I saw bodies. I think some people may have died."
Arash Kazerouni, from Edmonton, North London, 22, survived the Aldgate blast and said: "There was a loud bang and the train ground to a halt. People started panicking, screaming and crying as smoke came into the carriage. A man told everyone to be calm and we were led to safety along the track."
"Everyone was terrified when it happened. When they led us to safety, I went past the carriage where I think the explosion was. It was the second one from the front. The metal was all blown outwards and there were people inside being helped by paramedics.
Michael Henning was a subway commuter at the Aldgate/Liverpool station when the car next to his exploded. "I was being twisted and thrown to the ground. I thought I wasn't going to get out of this - whatever it was - I just didn't know. I thought that was it when it went all so dark.
"I am an extremely lucky man, I am very lucky indeed, especially as I saw what happened in the next carriage.
"The bomb must have been within 10 feet of me but that carriage took most of the blast and we were just showered in glass.
"Our carriage was smoke-filled, there was lots of dust, there was lots of panic. We could hear the screams from the carriage where the bomb had gone off - they were trapped in twisted metal."
Tanya Alleyway was also part of the Aldgate/Liverpool blast. "Everybody was absolutely terrified. You could hear the screaming from the carriages in front, because that was where the explosion had happened, and there was lots of injured people there. Nobody knew what was going on.
"The driver was trying to communicate with us, but the radio wasn't working.
"People were trying to open the doors and the windows to let the smoke out and were rocking the train, which already felt like it had come off its rails.
"So we were panicking that the train was going to get knocked over.
"It was just general chaos. I thought I was going to die when I saw the flames. I thought we were going to get engulfed by the flames or get overwhelmed by the smoke.
"I really didn't think we were going to get out. It hasn't quite sunk in, I think. It's the kind of thing where you see it on the news, but don't expect to be in it - and I was in it and it was horrible."
Ana Castro told BBC News her account of the explosion at the Liverpool subway station.
"People were screaming and shouting and saying things like I'm dying, I'm dying, please help me.
"I saw people just standing there in their underwear as if their clothes had been ripped off [by the explosion].
"I think I saw somebody who was dead it was just indescribable."
He said: "We just left Paddington station. About 15 seconds later there was some kind of explosion and we collided with another train. We were heading into the station when there was some kind of explosion or something. Everything went black and we collided into some kind of oncoming train. There was debris all over the trains. They evacuated us."
Clare Benson, 33, a city banker from Kensington, was on a tube at Edgware Road when she heard a massive explosion in the tunnel behind her. It was about 8.40 a.m.
"I was in the last carriage at the back of the train nearest the tunnel when I heard a huge bang - you could feel it. The lights went off for a couple of minutes and people were scared and wondering what to do. The drivers got out and were looking into the tunnel, then they announced that we should evacuate. My ears are still ringing and I was shaking."
Simon Corvett, 26, on an eastbound train from Edgware Road station, described "this massive huge bang ... It was absolutely deafening and all the windows shattered.
"The glass did not actually fall out of the windows, it just cracked. The train came to a grinding halt, everyone fell off their seats.
"You couldn’t really breathe and you couldn’t see what was happening. The driver came on the Tannoy and said ‘We have got a problem, don’t panic’.
"You could see the carriage opposite was completely gutted," he said. "There were some people in real trouble."
The explosions hit three subway stations and a double-decker bus in rapid succession between 8:30 and 9:30 a.m. London time. The bus explosion at Tavistock Square (search) was the last attack in the series.
"I was on the bus in front and heard an incredible bang, I turned round and half the double decker bus was in the air," Belinda Seabrook told Press Association, the British news agency.
Jay Kumar, a business owner near the site of the blast that destroyed a double-decker bus at Russell Square in central London, said he ran out of his shop when he heard a loud explosion. He said the top deck of the bus had collapsed, sending people tumbling to the floor.
"A big blast, a big bomb," he told The Associated Press. "People were running this way panicked. They knew it was a bomb. Debris flying all over, mostly glass."
Philippe Palmer, 42, from London was standing at a bus stop near Tavistock Square when he saw the bus explode in front of him.
"The bus was stuck in traffic just the same as any other morning. In a split second, there was a loud noise like a sonic boom and the top of the bus peeled off like a sardine tin."
"About five or six people were thrown out of the top of the bus along with debris. The whole place was covered in smoke and people were staggering out of the bus door. They were very disorientated."
"One minute it was a bus and the next minute we could not take in what had happened."
John Maingay saw the double decker bus in Tavistock Square explode. "I had just come out of my office to talk to colleagues about the news of an explosion in Liverpool Street.
"Literally at that moment there was a huge "boom" outside.
"I knew it was a bomb straight away. There was that smell of an explosion that accompanied it.
"I saw lots of debris fly past the window, including one huge chunk. It must have been the roof of the bus.
"All non-medical staff, myself included, were evacuated out the back of the building, while doctors working in the building immediately went to the aid of the casualties.
"Some were taken into the building and treated. Some of the building was also used as morgue.
"I'm not sure how many died. "
David Jones was on the bus in Tavistock Square when the bomb was deployed. "There was not a lot of fire but there was the smell of an explosion and at that point people wanted to walk away from what they had seen.
"There was no glass falling... there was a thud and the roof had come off.
Geraldine Fourmon was also in Tavistock Square to witness the explosion of the bus. "There was a big bang. After the smoke went away I realized there was a double decker bus exploded. People were running towards me screaming and crying.
"I saw at least five people jump from the top deck of the bus. Half of it was blown away. They were jumping onto the street to escape.
"It was such a big explosion and the bus was packed because the tube was closed. People were covered with dust and debris. I didn't see any blood."
Associated Press, Sky News, BBC News, London Times, and Press Association Contributed to this story.