China cracks down on chemical plants after blasts kill 56

China has ordered a nationwide check on dangerous chemicals and explosives following the 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.

According to latest reports, fires are still burning 36 hours after the blasts, and chemical experts are testing for toxic gases (See: Massive explosions kill 50, injure 700 in Tianjin, China).

There was one bright moment today 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.

The cause of the blast is still being investigated.

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 also "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.

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

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 has 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 miles) away from public buildings and main roads.

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.

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.

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 for 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.