Officials from the Chinese city of Tianjin, where two huge blasts killed 50 people, said they had discussed tightening safety standards with companies at the port just one week before the incident.

The explosions tore through the industrial area containing toxic chemicals and gas, killing at least a dozen firefighters and injuring 700 people, officials and state media said.

The People’s Daily newspaper said four fires were still burning.

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The Tianjin Administration of Work Safety posted a notice about the meeting with companies handling dangerous chemicals at the port on its website on August 6.

It did not give a specific date of when the meeting took place.

Despite the devastation, the port was operating normally, a port official said. Tianjin port is the gateway to northern China’s industrial belt.

Xinhua said the explosions, the first equivalent to 3 tonnes of TNT and the second to 21 tonnes of TNT, ripped through a warehouse.

It identified the owner of the warehouse as Tianjin Dongjiang Port Ruihai International Logistics.

The company’s website said it was a government-approved firm specialising in handling “dangerous goods”.

Company officials could not immediately be reached for comment.

According to an assessment by government environmental inspectors published in 2014, the facility was designed to store several dangerous and toxic chemicals including butanone, an explosive industrial solvent, sodium cyanide and compressed natural gas.

CCTV said at least one person at a “relevant company” had been detained.

The blasts on Wednesday night were so large they were seen by satellites in space and the impact was so great the blasts sent shockwaves through apartment blocks kilometres away in the port city of 15 million people.

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

Vast areas of the port — the tenth largest in the world — were devastated, crumpled shipping containers were thrown around like match sticks, hundreds of new cars were torched and port buildings left as burnt-out shells, witnesses said.

Tianjin authorities said 12 firefighters were among the 44 killed.

Charred remains of new cars are after an explosion tore through the parking lot. Photo: AAP

The cause of the blasts was unknown but industrial accidents are not uncommon in China following three decades of breakneck economic growth.

The state-run Beijing News earlier cited Tianjin fire authorities as saying they had lost contact with 36 firefighters, and that another 33 were among the hundreds of people being treated in nearby hospitals.

The official Xinhua news agency said 1,000 firefighters and more than 140 fire engines were struggling to contain a blaze in a warehouse that contained “dangerous goods”.

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

Several fire trucks had been destroyed and nearby firefighters wept as they worked to extinguish flames, the Beijing News reported.

President Xi Jinping demanded that authorities “make full effort to rescue and treat the injured and ensure the safety of people and their property”.

Mr Xi said in a statement carried by official media that those responsible should be “severely handled”.

Anxious residents rushed to hospitals to seek news about injured loved ones. Dozens of police guarded the entrance of the TEDA hospital, a witness said.

Pictures on Chinese media websites showed residents and workers, some bleeding, fleeing their homes. Xinhua said people had been hurt by broken glass and other flying debris.

Grey clouds of smoke billowed above the blast site and several trucks carrying paramilitary police — wearing masks to protect them from potentially toxic smoke — headed to the area.

The blasts shattered windows in buildings and cars and knocked down walls in a 2-km radius around the site.

Tianjin, south-east China. Photo: Mapbox