The devastation of the Tianjin port explosions

More than a thousand firefighters were sent in, but they were stopped as authorities tried to figure out which chemicals were burning – and their risk. Ca(C2) and TDI react violently with water and reactive chemicals, with risk of explosion. Seventy of them are in critical condition, Xinhua said, citing reports of local authorities.

It is also one of China’s more modern cities and is connected to the capital by a high speed rail line.

Speaking in English, the man and woman behind the camera suggest that the fire “might be at a gas station” before the explosions start.

Under Chinese regulations, warehouses stocking unsafe materials must be at least 1km away from surrounding public buildings and main roads, it said, but there were two residential compounds and several main roads within that distance.

State news agency Xinhua reported that rescue workers were “racing against the clock to save the injured and contain fires”, after the massive blasts.

At one building, on the side facing the blast, every single window is blown out.

Officials said Zhou had no recollection of when he reached the scene, and it was not clear whether he was among the first responders to the site who were caught up in the giant blasts, or if he arrived some time later. “It wasn’t that the firefighters were stupid”, Mr Lei said, adding it was a large warehouse and they did not know exactly where the calcium carbide was.

Meanwhile, more than 200 nuclear and biochemical experts from the Chinese military and a team from the global Atomic Energy Agency’s Beijing environmental emergency response centre are assessing the area surrounding the blasts.

Oil tanker arrivals and departures were also disrupted.

State broadcaster China Central Television (CCTV) said at least one person from the “relevant company” had been detained for questioning. The company was identified as Tianjin Dongjiang Port Rui Hai worldwide Logistics Co. Ltd.

“The volatility of the goods means the fire is especially unpredictable and unsafe to approach”, Xinhua said.

Internet videos showed fireballs shooting into the sky and the US Geological Survey registered the blasts as seismic events.

In the past decade, around 285 Fortune 500 companies have set up bases in Binhai, which is a new growth pole in China and is a hub of advanced industry and financial activity.

Seven people were killed and 300 injured when a shipment of flammable materials exploded.

The injured were taken to different hospitals in the city, with many reported to be suffering from cuts caused by broken glass.

Chinese President Xi Jinping and Premier Li Keqiang have vowed to investigate the accident.