China warns of change of wind spreading toxic substances at blast site

China warned residents near the site of two huge explosions who had taken refuge in a school to evacuate on Saturday after a change in wind direction stoked fears that toxic particles could be blown inland.

The evacuation came as a fire broke out again at the site of Wednesday's deadly blast in the northeastern port city of Tianjin, a warehouse specially designed to store dangerous chemicals, the official Xinhua news agency said.

Evacuees were advised to wear long trousers and face masks, according to a post on the official microblog of the Tianjin branch of the National Health and Family Planning Commission of China.

But there was no sense of panic on the streets, witnesses said.

Chinese police confirmed for the first time the presence of deadly sodium cyanide at the site of the blast that killed 85 people, state media said, as a series of new, small explosions were heard and small fires broke out.

Police confirmed the presence of the chemical, fatal when ingested or inhaled, "roughly east of the blast site", the state-run Beijing News said.

It did not say how much had been found or how great a risk it posed but residents expressed concern about the air and water. "I do feel a bit afraid," said construction worker Li Shulan, 49, when asked about the air quality. "It definitely doesn't feel good. As you can see our boss is making us wear masks." An area three km (two miles) from the site was cordoned off, the Beijing News said.

There were about seven small explosions in the area on Saturday, according to a post on the micro-blog of the official China Central Television. A Reuters witness said a fresh blaze ignited cars in a parking lot next to the blast site. The cause was not immediately clear. State media carried reports of other fires in the area.

A retired environmental official earlier told reporters that air pollution posed no risk. Harmful substances could not be detected in the air from 17 monitors placed around the city, he said.

About 6,300 people have been displaced by the blasts with around 721 injured and 33 in serious condition, Xinhua said. Shockwaves from the explosions were felt by residents in apartment blocks kilometres away in the city of 15 million people. Twenty-one of the dead were fire fighters.

About a dozen family members of missing fire fighters tried to storm a press conference, angry at a lack of information about their loved ones. "We have gone to each and every hospital by ourselves and not found them," said Wang Baoxia, whose elder brother is missing. "There is no government official willing to meet us. Not even one," she said. Relatives said around 25 fire fighters they said were missing were young contract workers not part of official city fire brigades.

Media have said such fire fighters in China, often only on two-year contracts, lack training as new recruits.

After Wednesday's blasts, fire crews were criticised for using water to douse flames which may have contributed to the blasts given the volatile nature of the chemicals involved.

Industrial accidents are not uncommon in China following three decades of fast growth. A blast at an auto parts factory killed 75 people a year ago.