Armed police were carrying out evacuations within 3km of the blast site on Saturday after highly poisonous sodium cyanide was found, the Beijing News said.
The blaze ignited again at the warehouse where the blasts struck on Wednesday night, with several small blasts heard by reporters from the Xinhua state news agency.
"Out of consideration for toxic substances spreading, the masses nearby have been asked to evacuate," Xinhua reported.
Authorities announced on Saturday that the death toll has risen to 104, with more than 700 others still being treated in hospitals, including 25 who are in critical condition and 33 who are in serious condition.
A survivor was pulled from a shipping container on Saturday morning, state media reported. His identity was not immediately known. Television video showed the man being carried out on a sketcher by a group of soldiers wearing gas masks.
Fears over safety after massive explosion in China
A team of chemical experts has been called in to the site to test for toxic gases.
Shockwaves from the blasts late on Wednesday were felt by residents in apartment blocks kilometres away in the city of 15 million people.
Furious residents and victims' relatives railed against authorities outside a news conference on Saturday for keeping them in the dark as criticism over transparency mounted.
Residents and relatives were prevented from entering the press conference and could be heard shouting outside.
"Nobody has told us anything, we're in the dark, there is no news at all," screamed one middle-aged woman, as she was dragged away by security personnel.
The man survived for three days in a shipping container following the blasts [Reuters]
China has a patchy industrial safety record and the disaster has raised fears of toxic contamination after officials said they were unable to identify precisely what chemicals were at the site at the time.
Tianjin work safety official Gao Huaiyou listed a host of possible substances at the briefing, adding that the firm's recent large exports had included sodium bisulfide, magnesium, sodium, potassium nitrate, ammonium nitrate, and sodium cyanide, among others.
China on Friday defended the work of firefighters who initially hosed water on a blaze in a warehouse storing volatile chemicals, a response foreign experts said could have contributed to the explosions.
In pictures: The deadly inferno
The explosions have disrupted the flow of cars, oil, iron ore and other items through the world's 10th largest port.
The blast sent shipping containers tumbling into one another, leaving them in bent, charred piles.
Rows of new cars, lined up on vast lots for distribution across China, were reduced to blackened carcasses.
Tianjin is the 10th largest port in the world by container volume and the seventh largest in China, according to the World Shipping Council, moving more containers than the ports of Rotterdam, Hamburg and Los Angeles.
It handles vast quantities of metal ore, coal, steel, cars and crude oil.
Authorities have only released limited information about the accident, a criticism often levelled at Chinese officials in the aftermath of disasters, and restricted discussion of it online.
More than 360 social media accounts have been shut down or suspended for "spreading rumours" about the blasts, Xinhua reported citing the Cyberspace Administration of China.
Source: Al Jazeera and agencies
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