SHOCKING aerial photos reveal the full extent of the two deadly Tianjin chemical explosions which have left at least 112 dead.

Chinese authorities ordered the evacuation of residents within a 3km radius of the warehouse that exploded, as police confirmed the presence of tonnes of the highly toxic chemical sodium cyanide.

Shi Luze, chief of the general staff of the Beijing military region, said cyanide had been identified at two locations in the blast zone.

Sodium cyanide is a toxic chemical that can form a flammable gas upon contact with water.

“The volume was about several hundreds of tonnes according to preliminary estimates,” he said.

Several hundred tonnes would be a clear violation of rules cited by state media that the warehouse could store no more than 10 tonnes at a time.

The comments were the first official confirmation of the presence of the chemical at the hazardous goods storage facility at the centre of the blast.

A military team of 217 chemical and nuclear experts was deployed early on, and earlier Chinese reports said 700 tonnes of sodium cyanide were at the site.

Tianjin environmental official Bao Jingling said authorities temporarily detected the highly toxic hydrogen cyanide in the air slightly above safety levels at two locations.

Bao said the contamination on Saturday afternoon, at four per cent and 50 per cent above the safety level, was no longer detectable later on Saturday.

“These levels are actually very low,” he said.

Bao said the cyanide was yet to be detected in water samples.

Officials have called in experts from producers of the material to help handle the toxic chemicals.

The country’s top prosecuting office announced that it was setting up a team to investigate possible offences related to the massive blasts, including dereliction of duty.

Zhi Feng, general manager of the warehouse’s operator, Ruihai International Logistics, has been under police watch while he receives medical treatment to ensure he does not flee during an investigation, state media reported.

Zhi was hospitalised after being injured in the disaster.

Authorities have repeatedly sought to reassure the public, insisting that despite the presence of some pollutants at levels above normal standards, the air in Tianjin remains safe to breathe.

Chinese Premier Li Keqiang arrived in Tianjin on Sunday afternoon to direct rescue efforts, official media reported.

Pictures showed the Communist Party number two within 1km of the blast site, dressed in an ordinary shirt and not wearing a mask.

But the official Xinhua news agency reported late on Saturday that cyanide density in waste water had been 10.9 times the standard on the day after the explosions.

It has since fallen, but was still more than twice the normal limit.

Environmental campaign group Greenpeace said on Sunday it had tested surface water for cyanide at four locations in the city and had not detected high levels of the chemical.

“These results show that local water supplies are not currently severely contaminated with cyanide,” it said, but reiterated its call for comprehensive tests on the air and water and for publication of the results.

Steve Ra, an American who was evacuated by his employer to another area of Tianjin, said he was worried about the potential health effects of the blast.

“The main concern is just the air,” Ra said.

Tianjin residents, relatives of the victims and online commentators have slammed local authorities for a lack of transparency, and at one point tried to storm a news conference on Saturday.

The government has moved to limit criticism of the handling of the aftermath, with a total of 50 websites shut down or suspended for “creating panic by publishing unverified information or letting users spread groundless rumours”, according to the Cyberspace Administration of China.

Critical posts on social media have also been blocked, and more than 360 social media accounts have been punished.

Nearly 100 people remain missing after Wednesday’s disaster, including 85 firefighters.

Eighty-eight unidentified corpses have so far been found and more than 700 people have been hospitalised.

Angry relatives of the missing firefighters and local residents whose homes were destroyed by the blasts showed up at a government news conference on Sunday to demand information and accountability