Huge explosions in a warehouse district sent up massive fireballs that turned the night sky into day, killing at least 44 people and injuring hundreds in the Chinese port city of Tianjin, officials and witnesses said Thursday. Twelve of the people killed were firefighters.

Thirty-two people were in critical condition and 283 others hospitalized following the explosions late Wednesday, the official Xinhua News agency said. In all, more than 400 people were injured, it said. The Beijing News newspaper said on its website that nine firefighters were among the dead in the city of 15 million, 115 kilometres southeast of Beijing.

The explosions knocked off doors of buildings in the area and shattered windows up to several kilometres away.

"I thought it was an earthquake, so I rushed downstairs without my shoes on," Tianjin resident Zhang Siyu, whose home is several kilometres from the blast site, said in a telephone interview with The Associated Press.

"Only once I was outside did I realize it was an explosion. There was the huge fireball in the sky with thick clouds. Everybody could see it."

China: the explosion in <a href="https://twitter.com/hashtag/Tianjin?src=hash">#Tianjin</a> Binhai New Area <a href="http://t.co/Hhadc4am0y">pic.twitter.com/Hhadc4am0y</a> via <a href="https://twitter.com/thelastnext">@thelastnext</a> —@NewsRevo

Zhang said she could see wounded people weeping. She said she did not see anyone who had been killed, but that she "could feel death."

There was no indication of what caused the blasts, and no immediate sign of any large release of toxic chemicals into the air. Beijing News said there was some unidentified yellow foam on the ground at the site, although it was not clear if this was contamination or part of the fire-fighting efforts.

"It was like what we were told a nuclear bomb would be like," said truck driver Zhao Zhencheng, who spent the night in the cab of his truck after the blasts. "I've never even thought I'd see such a thing. It was terrifying, but also beautiful."

Two large explosions

Police in Tianjin said an initial blast took place at shipping containers around 11:30 p.m. local time in a warehouse for hazardous materials owned by Ruihai Logistics, a company that says it's properly approved to handle hazardous materials. State media said senior management of the company had been detained by authorities, and that President Xi Jinping has demanded severe punishment for anyone found responsible for the explosions.

An injured man rests near the explosion site in Binhai new district in Tianjin, China on Thursday. (Damir Sagolj/Reuters)

The National Earthquake Bureau reported two major blasts before midnight, the first with an impact equivalent to 2.7 tonnes of TNT, and the second with the equivalent of 19 tonnes. The official Xinhua News agency said the initial explosion triggered other blasts at nearby businesses.

The explosions took place in a mostly industrial zone, with some apartment buildings in the vicinity. Buildings of a half-dozen other logistics companies were destroyed in the blasts, and more than 1,000 new Renault cars were left charred in nearby parking lot, Beijing News said.

Local media reported that up to 1,000 brand new Renault cars were destroyed by the blasts. (Greg Baker/Getty)

The Tianjin municipality said more than 1,000 firefighters were sent to fight the ensuing fire, which was mostly under control by morning.

As is customary during disasters, Chinese authorities tried to keep a tight control over information. Police kept journalists and bystanders away with a cordon about 1 or 2 kilometres from the site. On China's popular microblogging platform of Weibo, some users complained that their posts about the blasts were deleted, and the number of searchable posts on the disaster fluctuated, in a sign that authorities were manipulating or placing limits on the number of posts.

The website of the logistics company became inaccessible Thursday.

Photos apparently taken by bystanders and circulating on microblogs show a gigantic fireball high in the sky, with a mushroom cloud above. Other photos on state media outlets showed a wall of flames that painted the night sky bright orange, with tall plumes of smoke.

'The sky just lit up brighter than day'

About 2 kilometres from the explosion site is the luxury Fifth Avenue apartment complex on a road strewn with broken glass and pieces of charred metal thrown from explosion. Like surrounding buildings, the Mediterranean style complex had all its windows blown out, and some its surfaces were scorched.

"It's lucky no one had moved in," said a worker on the site, Liu Junwei, 29. "But for us it's a total loss. Two years hard work down the drain."

"It had been all quiet, then the sky just lit up brighter than day and it looked like a fireworks show," said another worker on the site who gave just his surname, Li.

Explosion rocks north China port city of Tianjin 0:50

At the nearby Taida Hospital as dawn broke, military medical tents were set up. Photos circulating online showed patients in bandages and with cuts.

State broadcaster CCTV said six battalions of firefighters had brought the ensuing fires under control, although it was still burning in the early hours of Thursday.It says the firefighters were combing the neighbourhood for possible injured residents.

Video: CCTV captures moment <a href="https://twitter.com/hashtag/blast?src=hash">#blast</a> occurred in Chinese city of <a href="https://twitter.com/hashtag/Tianjin?src=hash">#Tianjin</a> <a href="https://t.co/gmQHGtUPe4">https://t.co/gmQHGtUPe4</a> —@XHNews

Ruihai Logistics says on its website — before it was shut down — that it was established in 2011 and is an approved company for handling hazardous materials. It says it handles more than 900,000 tonnes of cargo annually.

Tianjin is one China's most important ports, as well as one of the country's more modern cities. It is connected to Beijing by a high speed rail line.