The Chinese authorities have ordered the evacuation of residents within a 3km radius of the Tianjin blast site over fears of chemical contamination.
The evacuations came after an apparent change in wind direction, and as police confirmed the highly toxic chemical sodium cyanide was found near the site.
A man was found alive 50m from the blast core, Xinhua news agency said.
At least 104 people are reported to have died in the giant blasts in the north-east Chinese port on Wednesday.
People sheltering at a school used as a safe haven since the disaster have been asked to leave wearing masks and long trousers, reports say.
The order came after the wind apparently changed direction, prompting fears that toxic particles that would have previously been blown out to sea could be blown inland.
Anti-chemical warfare troops have entered the site.
The People's Daily newspaper tweeted that they had been sent to handle highly toxic sodium cyanide which had been found there.
The discovery was confirmed by police "roughly east of the blast site" in an industrial zone, state-run Beijing News said.
Officials had until then only confirmed the presence of calcium carbide, potassium nitrate and sodium nitrate. Calcium carbide reacts with water to create the highly explosive acetylene.
Officials have so far insisted that air and water quality levels are safe.
Meanwhile Chinese President Xi Jinping urged the authorities to learn the "extremely profound" lessons and keep "safe growth" and "people's interest first" in mind to avoid similar accidents.
http://www.bbc.com/news/world-asia-china-33945293