At a barrier on the edge of the evacuation zone masks were distributed to emergency personnel and police turned back anyone else, as at least 20 fire engines streamed in.
The area itself was already largely deserted, many of the buildings within it ruined, and an acrid smell hung in the air.
One couple carrying suitcases confirmed from behind their masks only that they lived within it, before leaving.
Officials said earlier that specialists from sodium cyanide producers were being sent in to the devastated industrial area where the blasts occurred.
Reports have said there could have been as much as 700 tonnes of the substance — exposure to which can be fatal — at the site.
Soldiers trained in anti-chemical warfare techniques were also deployed.
Authorities have struggled to identify the substances present at the scene, sparking fears and scepticism among residents of Tianjin, which has a population of 15 million.
Host of possible substances
At a news conference, Tianjin work safety official Gao Huaiyou listed a host of possible substances that may have been at the site at the time of the explosions.
Personnel from sodium cyanide producers had been called in “because they are experts on the chemical’s nature and the ways to deal with it”, he added.
A sewage pipe where the chemical had reportedly been detected had been sealed off, he said.
Authorities had repeatedly said beforehand that air quality in the city generally met requirements, although levels of some pollutants exceeded regulations.
Questions have also been raised over whether firefighters responding to an initial blaze at the warehouse could have contributed to the detonations by spraying water over substances that react explosively to it.
One senior official insisted firefighters had followed the proper procedures.
“We knew there was calcium carbide, but we don’t know whether the calcium carbide exploded and caught fire,” Lei Jinde, the head of the firefighting department at Tianjin’s public security bureau, said in an interview published by Xinhua.
Lei said that the facility was also listed as holding ammonium nitrate and potassium nitrate.
‘In the dark’
There were 21 firefighters among the dead, authorities said, and 721 people had been hospitalised, 25 of whom were in critical condition.
China has a dismal industrial safety record and authorities have only released limited information about the accident, a criticism often levelled at Chinese officials in the aftermath of disasters.
Furious victims’ relatives railed against officials outside a news conference Saturday for the lack of transparency and information.
“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 People’s Daily said earlier that the facility’s construction “clearly violated” safety rules, in particular those that require warehouses stocking dangerous materials to be at least one kilometre (0.6 miles) from surrounding public buildings and main roads.
“I would rather not believe they are true when I see a series of rumours, but the cruel reality has proved their authenticity,” Chinese director Yang Li, the winner of a Silver Bear at the 2013 Berlin Film Festival, wrote in a post on microblogging platform Sina Weibo.
“Why did they (the government) cover it up?”
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.
Popular verified bloggers had also made “irresponsible” comments about the blasts, such as comparing them to the atomic bombs dropped on Japan during World War II, it added.
Chinese authorities and Internet companies operate a vast censorship system and while there has been extensive discussion of the explosions, it has been confined within set boundaries.