Media playback is unsupported on your device Media caption An eyewitness captures the fear of those watching the explosions

China has ordered a nationwide check on dangerous chemicals and explosives following explosions in Tianjin that left 56 dead and 721 injured.

China's cabinet also ordered officials to "crack down unwaveringly on illegal activities to ensure safety".

The operators of the Tianjin site have been accused of "clearly violating" safety rules.

Fires were still burning 36 hours after the blasts, and chemical experts are testing for toxic gases.

There was one bright moment on Friday when 19-year-old firefighter Zhou Ti was pulled from the rubble alive, state-run news agency Xinhua reported. But 21 firefighters are reported to be among the dead and several more are missing.

Media playback is unsupported on your device Media caption Military chemical experts are testing for toxic gases and rescuers have been told to wear protective clothing

The cause of the blast is still being investigated.

Cyanide fears

In a report, Xinhua said the cabinet, the State Council, had ordered "governments at all levels to reinforce the safety management on dangerous chemicals and explosives".

They should "firmly implement special regulatory measures for highly toxic chemicals such as cyanide, as well as inflammable and explosive materials".

The reference to cyanide followed reports in the People's Daily that 700 tonnes of sodium cyanide were at the Tianjin site. Ammonium nitrate may also have been present.

Officials have only confirmed that calcium carbide, potassium nitrate and sodium nitrate were at the warehouse.

Image copyright AP Image caption Firefighter Zhou Ti is treated in hospital after being pulled out of the rubble on Friday

Image copyright AFP Image caption Many residents have taken to wearing gas marks despite being told the air is safe

Chinese officials, though, have admitted there are discrepancies between accounts from the company and from customs, and that damage to company offices had made it hard to identify the chemicals.

More than 200 chemical and biological experts from the military are on site but officials insist that the air and water quality levels in Tianjin are safe.

However, the People's Daily quoted the Beijing News as saying that sodium cyanide had now been detected in the sewage and leakage had been confirmed.

Many residents could be seen wearing air-filtering masks. One, Ma Wiehan, told Associated Press: "I don't usually wear a mask but I don't quite trust what the government says."

People's Daily said the Tianjin facility, operated by Ruihai Logistics, had "clearly violated" safety rules that say dangerous materials must be stored at least 1km (0.6 mile) away from public buildings and main roads.

Media playback is unsupported on your device Media caption Dashboard camera captures China blast shockwave

Media playback is unsupported on your device Media caption Aerial views of the site of the explosion in Tianjin

State media said the manager of the Ruihai Logistics site had been detained.

In its new directive, the State Council "urged governments at all levels to learn bitter lessons from the two massive blasts and to crack down unwaveringly on illegal activities to ensure safety".

"The lessons are extremely profound," it said.

'No-one knew'

Fire officials have defended the actions of the team who responded to the initial report of a fire on Wednesday night, amid suggestions that using water on some of the chemicals could have led to the blasts.

Calcium carbide reacts with water to create the highly explosive acetylene.

Image copyright Reuters Image caption Notices for missing people at a school-turned-evacuation centre

Image copyright AFP Image caption More than 720 people have been injured

Image copyright EPA Image caption Prayer candles are lit for the victims of the Tianjin blasts at the city's Chaoyin Temple

Fire department official Lei Jinde said: "We knew there was calcium carbide inside but we didn't know whether it had already exploded. At that point no-one knew, it wasn't that the firefighters were stupid."

They would not have sprayed water on calcium carbide, he said, although he admitted it was a large warehouse and the team could not be sure where that substance was.

Chemical experts suggest an acetylene blast could then have detonated ammonium nitrate to create a much larger blast.

There were two explosions. The first was equivalent to about three tons of TNT, the second - some 30 seconds later - was equivalent to 21 tons.

From his hospital bed, rescued firefighter Zhou Ti said: "I was knocked on to the ground by the first blast. I covered my head and don't know what happened after that."

Thousands of comments have been posted on Chinese social media hailing the firefighters' bravery.

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Fires are still sending plumes of smoke over the destroyed buildings, burned-out vehicles and crumpled shipping containers that bore the brunt of the explosions.

The Tianjin Port Group Company said dozens of its employees remained unaccounted for, according to Xinhua.

Of the 721 people injured, 25 are in critical condition and 33 are serious.

Officials said more than 6,000 residents forced to leave their homes had been relocated at several nearby schools that are being used as temporary shelters.

Rows and rows of cars were incinerated - Renault alone said it may have lost some 1,500 vehicles.