It was an emergency drill, yet the scene of hundreds of firefighters, police officers and other first responders hustling around the World Trade Center site Sunday evoked the aftermath of the Sept. 11, 2001 attacks.

Firefighters carried oxygen tanks, hoses and heavy axes into an underground train station, while police and other emergency personnel helped those playing injured — all part of a large disaster response exercise at ground zero.

More than 800 first responders participated in Sunday's mock terrorist attack, which simulated an explosion on a New Jersey-bound PATH commuter train in a tunnel. The police, firefighters and other emergency personnel joined about 150 volunteers, who posed as injured passengers smudged with grime and fake blood.

The hundreds of first responders represented the largest police and firefighter presence at the trade center site since the aftermath of Sept. 11, 2001. The purpose of the drill was to improve interagency cooperation in the event of a real disaster.

"The motto for today is: You can never be too prepared," said Chris Ward, executive director of the Port Authority of New York and New Jersey, which runs area transit hubs and owns the trade center site. "We will evaluate how well we did prepare, how well we performed, find wherever we did make mistakes and how we can improve."

The two-hour drill recalled the July 7, 2005, bombings on the London subway system more than the 2001 attack on the twin towers.

In the drill, two bombs went off at 8:01 a.m. EDT (0001 GMT) on a train in the tunnel between Manhattan and New Jersey.

"Smoke filled the tunnel, and we had some 700 to 800 passengers on this train," said Joseph Bruno, New York City's commissioner of emergency management.

PATH service was suspended during the exercise, and streets around the trade center site were blocked off.

Participating agencies included New York City's police and fire departments and its Office of Emergency Management and Department of Health and Mental Hygiene, as well as the police department of the Port Authority, which operates the PATH trains.

"The main thing we're trying to evaluate is the ability of all these agencies to work together," Bruno said.

Poor communication and jurisdictional infighting between the police and fire departments impeded rescue efforts when the twin towers were struck in 2001, and Bruno said he was confident that the departments are better at working together now.

"I think we are at a totally different place than we were at the time of that incident, and that's good," he said.

Firefighters went into the PATH tunnel to extinguish fires caused by the drill's explosions and to rescue passengers. There were 10 fake fatalities. Most of the injured passengers were able to walk out of the station, but about 20 were carried out on red stretchers.

Chief Joseph Pfeifer, head of counterterrorism for the Fire Department of New York, said firefighters used lightweight aluminum carts that fit onto train tracks to transport the most severely injured.

He said the carts were developed after the 2005 London bombings because "it's very labor intensive to carry someone out."

Other drills staged since the 2001 terror attacks in New York City have included a simulated response to a hazardous chemical spill and an explosion on an Amtrak train at Penn Station.

"If we're going to make mistakes we want to make them here, we want to learn from them, we want to build them into our plans, so when there is a real situation we respond appropriately and all the kinks in the system have been worked out," said Deputy Mayor Ed Skyler.

Richard Falkenrath, the police department's deputy commissioner for counterterrorism, added, "It's an important thing to be doing, and we will learn a lot of lessons from it I have no doubt."

Officials bought television ads and plastered train stations with posters to warn downtown Manhattan residents of the drill. The warnings for those in the area came after a Department of Defense-arranged flyover by a jet above downtown Manhattan last month panicked thousands of Wall Street workers and residents.

Bruno said the flyover "pointed out the need for people to know as much as possible."

"We would not want folks to wake up here and see all this equipment and wonder," he said.