Chinese authorities have evacuated a three-kilometre zone around the Tianjin explosion site over fears of chemical contamination.
The move came as angry family members of firefighters missing after the blasts that rocked the Chinese port city stormed a government news conference, demanding information on their loved ones.
Authorities said in the news conference that the death toll after Wednesday's inferno and blasts has climbed to 85, including 21 firefighters - making the disaster the deadliest for Chinese firefighters in more than six decades.
A number of firefighters remain missing, and 720 people were injured in the rapid succession of explosions that began with a fire among shipping containers containing hazardous material at a warehouse.
Police and military staff are deployed at checkpoints leading to the explosion site, and helicopters are hovering above as fires continue to burn.
Authorities are yet to determine the full list of chemicals on site, but state media say there are large amounts of sodium cyanide, which is combustible upon contact with water.
A rapid succession of explosions - one equal to 21 tons of TNT - were sparked by the fire.
They struck a mostly industrial area late at night, otherwise the death toll could have been much higher, but the warehouse was close enough to homes to appear to fall foul of safety regulations, raising questions about whether it had been properly authorised.
Firefighters initially responded to a blaze at the warehouse and many of them were apparently killed by a series of explosions triggered 40 minutes after the fire was reported.
Tianjin Fire Department head Zhou Tian said the explosions occurred just as reinforcements had arrived on the scene and were getting to work.
"There was no chance to escape, and that's why the casualties were so severe," he said. "We're now doing all we can to rescue the missing."
Local officials have been hard-pressed to explain why authorities permitted hazardous goods warehouses so close to residential complexes and critical infrastructure.
They have also been publicly reticent about suspicions that firefighters may have sparked the explosions by spraying water on volatile chemicals.
Hazardous chemical warehouses must be at least 1,000 metres from public buildings, highways, railways and industrial enterprises under regulations enacted by China's State Administration of Work Safety in 2001.
But Google Earth shows that the Ruihai firm's two hazmat warehouses were less than 500 metres from the S11 Haibin Expressway, and within 500 metres of a 104,438-square metre apartment complex built by China Vanke, one of China's largest developers.
Vanke said it acquired the land before Ruihai Logistics began loading toxic substances in its warehouses one block away.