Chinese officials face a race against time to clear toxic chemicals from the site of the Tianjin warehouse explosion, amid fears the blast may have released hundreds of tons of toxic gas into the air.

Soldiers have joined rescue workers in gas masks and hazard suits in the port city where the death toll from Wednesday’s massive explosion has risen to 112. Another 95, the majority of whom were firefighters, remained missing.

Officials confirmed the warehouse where the blast occurred was used to house more than 100 tons of sodium cyanide, a potentially deadly substance.

The presence of the chemicals was confirmed by Shi Luze, the chief of staff of the People's Liberation Army's Beijing Military Region.

He said workers were trying to clear the area before possible rain showers, which could create toxic gas.

The site of the explosion in Tianjin (EPA)

Smoke billows from behind burnt out Volkswagen cars the second morning after a series of explosions at a chemical warehouse hit the city of Tianjin (AFP)

The government has faced calls to extend its 3km exclusion zone around the site, though Shi said the toxins represented no danger to people outside the evacuated area.

Fire crews were criticised for using water to douse flames in the initial fire which may have contributed to the blasts, given the volatile nature of the chemicals involved.

Greenpeace said tests around the blast site showed that water supplies were not severely contaminated with cyanide, but that they did not "disprove the presence of other hazardous chemicals in the water".

Tianjin Explosion - In Pictures Show all 14 1 /14 Tianjin Explosion - In Pictures Tianjin Explosion - In Pictures Tiajin Explosion A man wearing a mask walks past overturned shipping containers after explosions hit the Binhai new district in Tianjin. Two massive explosions caused by flammable goods ripped through an industrial area in the northeast Chinese port city of Tianjin late on Wednesday, killing 17 people and injuring around 400, official Chinese media reported. Tianjin Explosion - In Pictures Tianjin8.jpg A screen grab from taken from state broadcaster China Central Television (CCTV) footage on August 12, 2015 shows a huge explosion in the northern Chinese port city of Tianjin. Tianjin Explosion - In Pictures Tianjin Explosion Excavators work near the site of the explosions at the Binhai new district, Tianji Tianjin Explosion - In Pictures Tianjin Explosion A man who was injured following the massive explosions at the Binhai new district in Tianjin receives medical treatment at a hospital. Tianjin Explosion - In Pictures Tianjin Explosion View of the destruction after explosions in the port area of Tianjin, northern China, Tianjin Explosion - In Pictures Tianjin Explosion A emergency worker is lifted by a crane as smokes plumes from the explosion site in Binhai new district in Tianjin Tianjin Explosion - In Pictures Tianjin Explosion A damaged truck is seen on a highway near the site of the explosions at the Binhai new district in Tianjin Tianjin Explosion - In Pictures Tianjin Explosion Flames rise as a banner in the background reads "no illegal operations" at the site of a series of explosions in Tianjin, witnesses described a fireball from the blasts ripping through the night sky. Tianjin Explosion - In Pictures Tianjn Explosion Smoke rises from shipping containers after explosions at Binhai new district in Tianjin, China. Tianjin Explosion - In Pictures Tianjn Explosion Firefighters take a break after trying to put fire down at the explosion site in Binhai new district in Tianjin, Tianjin Explosion - In Pictures Tianjn Explosion A survivor talk on his mobile phone at the site of the explosions at the Binhai new district in Tianjin Tianjin Explosion - In Pictures Tianjin Explosion Firefighter's truck and other rescue vehicles are pictured as smoke rises among shipping containers after explosions at Binhai new district in Tianjin Tianjin Explosion - In Pictures Tianjn Explosion Damaged cars are seen near the site of explosions at the Binhai new district in Tianjin Tianjin Explosion - In Pictures Tianjn Explosion A paramilitary policeman wears a mask as he blocks the road leading to evacuated residential area and the explosion site in Binhai new district in Tianjin

"Greenpeace reiterates its call for authorities to implement a comprehensive survey of hazardous chemicals currently present in air and water supplies and make public all information," it said.

Shockwaves from the blast itself were felt by people in apartment blocks several kilometres from the warehouse, and the larger explosions registered as seismic events with the US Geological Survey.

More than 6,000 people have been displaced since, and a group sheltering in a school near the site was moved on Saturday for fear that a change in wind direction could bring toxic gases their way.

"I'm very worried that these dangerous chemicals will harm my health," said Zhang Yinbao, who works in the chemical industry and whose apartment building is only 800 metres from the blast site.