China has sent a team of military specialists in handling chemicals to the northern city of Tianjin, after warehouse explosions left at least 50 dead, state media report.
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.
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.
The blast was so big fireballs and explosions could be seen from space and such was the magnitude of the explosion it registered as seismic activity.
The explosion has left an apocalyptic landscape and fires that are still burning.
Radio New Zealand's Beijing correspondent Ryan Bridge told Morning Report some of those nearest the blast had "simply vapourised."
He said although the blast zone was largely a construction zone, and therefore there was little residential acomodation nearby.
"They were housed in temporary workers' accomodation and a lot of those went up in flames during the explosions."
Ryan Bridge said migrant workers represented many of those killed and injured.
He said chemical contamination was now a major concern among officials and rescuers.
"The warehouse was storing some very toxic chemicals and one of the major problems now is the air quality - there are reports of around a kilometer away from the blast site a pungent smell in the air; and people are really concerned about what exactly is in the air."
The warehouse stored cyanide and epoxyethane, a harmful gas that can cause cancer.
The warehouse that exploded is owned by a company called Ruihai Logistics.
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, 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 to each other like toy bricks.
Rows and rows of new cars were reduced to blackened husks.
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."
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.
Chinese Premier Li Kequiang has promised "open and transparent information disclosure" on the investigation.