China has sent a team of military chemical experts to the northern city of Tianjin, after explosions left at least 50 dead, state media report.
The blasts, late on Wednesday night, ripped through an industrial port area, destroying buildings, shipping containers and thousands of new cars.
It is not known what caused the blasts, nor whether chemicals have leaked.
More than 3,500 residents are spending the night in temporary shelters. Hundreds are injured, 71 critically.
State news agency Xinhua reports that rescue workers are “racing against the clock to save the injured and contain fires”, 24 hours after the massive blasts at a warehouse in the Binhai New Area.
Many of the wounded had glass or shrapnel cuts, skull injuries or fractures, Wang Siaojie of Teda Hospital said.
More than 200 experts in chemical materials from the Chinese army have arrived in Tianjin. Their first task was to test the air for toxic gases, Xinhua said.
Rescue teams were ordered to wear protective clothing, it added.
The warehouse that exploded is owned by a company called Ruihai Logistics, which handles toxic chemicals including sodium cyanide and toluene diisocyanate, according to reports.
The People’s Daily, the official newspaper of the Chinese Communist Party, reports that rescuers “are trying to remove all the 700 tons of sodium cyanide” stored at the site. Hydrogen peroxide had been prepared to detoxify the chemical, the paper says.
The Tianjin Port Group Company said dozens of its employees were unaccounted for, according to Xinhua.
Firefighters were already at the scene when the explosions took place.
They had been called to reports of a container fire, state media said. At least 17 firefighters are among the dead.
The two successive explosions, at 23:30 local time on Wednesday (15:30 GMT), caused a fireball visible from space and a blast wind that broke windows several kilometres away.
A large area of the port was devastated. Shipping containers were left buckled, bent and toppled on top of each other like toy bricks.
Row upon row of new cars were reduced to blackened husks.
Almost 10,000 vehicles were ruined, according to Chinese media, with Renaults and Volkswagens the worst affected.
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The head of Tianjin’s environmental protection bureau, Wen Wurui, said pollution levels were being monitored.
“It would be harmful if you breathe in [this toxic air] for a long time,” he said.
“But at present, it has not exceeded [the standard] too much based on our monitoring.”
Water discharge points to the sea had been closed, he said.
A man who was working as a security guard in a nearby factory told the BBC that he saw there was a fire, but did not expect explosions.
“Suddenly I heard a bang,” he said. “I lay down immediately, but I still got injured.
“My security booth was destroyed completely.”
Another injured man said after the explosion his mind went blank.
“My first reaction was to run,” he said. “I heard another burst. I was running away. I got blood all over my body.”
The blast ripped apart a nearby dormitory for migrant workers, who were forced to flee the collapsing building.
“I rolled off the bed after the first shockwave hit, so I scrambled to run for my life,” said resident Dan Agio.
“When I reached downstairs, the second blast happened. It’s as if the sky collapsed. In a blink of an eye, the roof fell.”
The editor of the BBC’s Chinese Service, Raymond Li, points out that 24 hours after the explosions, the cause still is not known.
Just a few days ago, city officials visited the industrial site to discuss safety standards, he says.
It is also becoming clear that the hazardous chemicals were stored closer to residential areas than they are legally allowed to be, he says.
Chinese Premier Li Keqiang has promised “open and transparent information disclosure” on the investigation.
The People’s Daily reported that officials had said the cause of the explosion would be figured out once the fire at the scene had been completely extinguished.
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