Chinese authorities ordered the evacuation of citizens within a radius of three kilometres from the site of the exploded warehouse in Tianjin over fears of chemical contamination with the highly toxic sodium cyanide.

The evacuation was necessitated after a change in the direction of wind and as reports emerged that sodium cyanide might have been stored in the warehouse, which exploded late on Wednesday.

The death toll from the two deadly explosions has increased to 85 people, Xinhua news agency informs.

The change in the direction of wind sparked fears that toxic particles could be blown inland and anti-chemical warfare troops were deployed to the site.

A total of 721 people have been hospitalised, 25 of them critically wounded, while 33 were in serious condition.

At least 21 firefighters are among the dead and unknown number remain missing.

The operators of the warehouse were accused of breaching safety rules.

Fire continues to rage and some of the damaged cars on the site are causing further explosions.