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.
At least 112 people died in the blasts, officials said on Sunday, and more than 700 have been hospitalised.
Officials have identified 24 of the dead, with 88 still to be identified.
Remarkably, a man was found alive just 50m from the blast core, Chinese state news agency Xinhua reported.
The man was able to talk when he was found and is now in hospital, according to the report.
People sheltering at a school used as a safe haven since the disaster have now been asked to leave wearing masks and long trousers, reports say.
The order came after a change in wind direction, prompting fears that toxic particles that would have been blown out to sea could be blown inland.
Troops equipped with chemical warfare protection have now entered the site of the blasts.
The People's Daily newspaper tweeted that the specialist troops had been sent to handle the highly toxic sodium cyanide found at the site.
Police said the discovery occurred "roughly east of the blast site" in an industrial zone, according to state-run Beijing News.
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.
What is sodium cyanide?
The chemical sodium cyanide is white crystalline or granular powder which can be rapidly fatal if inhaled or ingested, as it interferes with the body's ability to use oxygen.
It is mostly used in chemical manufacturing, for fumigation and in the mining industry to extract gold and silver.
It is soluble in water, and absorbs water from air, and its dust is also easy to inhale. When dissolved or burned, it releases the highly poisonous gas hydrogen cyanide.
Some fires have continued to smoulder and at least one reignited on Saturday. Xinhua said several cars at the site had "exploded again".
Of the 721 people injured, 25 are in critical condition and 33 are serious.
At least 21 firefighters are among the dead and an unknown number remain missing.
Dozens of relatives of the missing tried to disrupt a news conference given by officials on Saturday, demanding to know the fate of their loved ones.
"We have gone to each and every hospital by ourselves and not found them," Reuters news agency quoted Wang Baoxia, whose elder brother is missing, as saying.
"There is no government official willing to meet us. Not even one."
The operators of the Tianjin site have been accused of violating safety rules.
The Chinese government has ordered officials to make nationwide checks on dangerous chemicals and explosives and to "crack down unwaveringly on illegal activities to ensure safety"
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