The rapid chain of explosions that destroyed a warehouse district in the Chinese port of Tianjin could become one of the world's deadliest disasters for fire crews, with at least 21 firefighters confirmed dead and scores of others still missing.

Now questions are being raised about whether the crews were properly trained and equipped to deal with the emergency at a warehouse that stored a volatile mix of chemicals, including compounds that become combustible on contact with water.

For a third day Monday, angry relatives of the 64 missing firefighters flocked to a hotel to demand information about their loved ones from government officials.

"I've gotten no information from the authorities whatsoever," said Liu Runwen, whose 18-year-old son, Liu Zhiqiang, has been missing since he responded to the fire Wednesday night.

Liu said his son joined the force two years ago on the recommendation of a friend and embraced the danger despite safety concerns.

"He was proud to be a firefighter who could serve the people," Liu said.

The father had questions about whether his son was sufficiently prepared, and he complained that TV reports failed to mention contract firefighters like his son alongside full-fledged firefighters "as if they never took part at all."

As of Monday, 114 people had been confirmed dead in the blasts, which destroyed several warehouses, crumpled shipping containers and shattered windows several kilometers (miles) away. Police have cordoned off the area of still-smoldering fires in a mixed industrial and residential zone, and more than 6,000 people have been forced into temporary shelters or are staying with friends and family.

Also angry with authorities was Yang Jie, whose firefighter son, Yang Weiguang, is among the missing. The 23-year-old had joined just 10 months earlier after a two-year stint in the army.

"He didn't worry about his own safety when he became a firefighter, but he knew firefighters might face danger while carrying out rescue work," Yang said. "He never thought he would encounter such a huge accident."

Yang Weiguang is "a very good kid," his father said. "He doesn't drink or smoke or pick fights but really likes reading novels by foreign authors."

State media have already called the accident the single deadliest for firefighters since the founding of the People's Republic of China in 1949. The death toll for fire crews could go much higher if many of the 70 missing are confirmed dead.

Local officials have yet to comment on the possible cause of the explosion and the fire that preceded it. However, the Global Times newspaper, citing chemical industry experts speaking on condition of anonymity, said the blast was probably triggered by a flammable substance such as industrial alcohol stored on the site. Other reports suggested that high summer temperatures may have been a factor, along with the possibility of a chemical reaction sparked by water being sprayed by the firefighters.

Zhong Shengjun, a social scientist who studies industrial safety at Northeastern University in Shenyang, said "we can't rule it out that when firefighters tried to cool down the area, they sprayed some water on some alkali metals that should not be in contact with water. It's partly because the firefighters couldn't contact the executives of the warehouse in time so as to know exactly where different chemicals were placed."

"This disaster has exposed several problems, such as the poor management of dangerous chemicals. In theory, they should be stored by category and have clear signs placed on their containers indicating their basic features," he said.

China should have a system whereby dangerous chemicals are tracked on their containers by bar code, but that system has not yet been adopted at Chinese ports, Zhong said.

In the United States, firefighters regularly visit industrial sites to become familiar with hazardous materials and how they are used and stored.

"You need to know ahead of time what you're dealing with," said Glenn Corbett, associate professor of fire science at John Jay College of Criminal Justice in New York City.

However, Zhong said that because the Tianjin accident took place at transit warehouse in a loading area of the port, the material was there only temporarily, making it especially difficult to identify.

Corbett said that beginning in the late 1960s, American fire crews also established specialized hazardous-materials teams that are "trained to a much higher level" than regular firefighters.

Many of the Tianjin firefighters, including many of the dead, were not part of a full-time department, but rather had been hired on one-year contracts to act as a sort of auxiliary firefighting force. They did not enjoy the official perks and job security of the national firefighting team, which is itself an adjunct of the paramilitary People's Armed Police.

One of contract firefighters, 18-year-old Zhou Ti, survived only because he was buried so deeply under his colleagues' corpses.

About 40 minutes after the first reports of a fire, a sudden set of explosions — one equivalent to 21 tons of TNT — all but obliterated Zhou's squad. Rescuers pulled him out about 32 hours later.

"I was wondering what could be wrong with me. Why would people need to be saving me? And then it occurred to me that maybe I was in an incident," Zhou told state broadcaster CCTV in an interview from his bed at Teda Hospital, where he was in stable condition. Doctors refused requests by other media to interview him, citing the fear of infection to his damaged lungs.

A firefighter for just over a year, Zhou said he understood the risks of the job.

"Yes, I have a bit of fear, but it does not stop me from firefighting. I won't let my fear show. You do what you need to do," said Zhou, breathing with the help of a respirator, his face burned black by the explosion.

Knocked to the ground by the initial blast, Zhou said he tried to cover his head before blacking out. "I recall nothing after that," he said.

Just 24 of the accident's 114 confirmed victims have been identified. The force of the blast and heat of the fire make it unlikely that the bodies of the dead would remain intact.

The fate of the firefighters has captured the public imagination, with tributes streaming in from Premier Li Keqiang and other top officials.

One set of SMS messages reportedly sent between an unnamed firefighter and a friend has been circulated widely online. In it, the firefighter says one of his colleagues has just been killed. He also asks his friend to look after his father if he fails to return alive.

"If I don't come back," the unnamed firefighter wrote, "my dad is your dad."

State television said the man survived.

___

Associated Press writers Didi Tang and Ian Mader and researcher Henry Hou in Beijing, video journalist Paul Traynor in Tianjin and Deepti Hajela in New York contributed to this report.