Two massive explosions caused by flammable goods ripped through an industrial area in the northeast Chinese port city of Tianjin late on Wednesday, Aug 13, killing 17 people and injuring as many as 400, Reuters said, citing official Chinese media reports.

Authorities had lost contact with 36 firefighters on the scene, according to the official Beijing News newspaper.

The force of the explosions unnerved residents across much of the city of 15 million people, with some posting videos on the Internet that showed giant fireballs shooting into the sky and shockwaves buffeting apartment blocks and cars.

China Central Television (CCTV) said the blasts erupted in a shipment of explosives at around 11:30 pm local time (1130 EDT), triggering a shockwave that was felt kilometers (miles) away. The second blast came roughly 30 seconds after the first.

Xinhua state-run news agency said the explosions ripped through a warehouse storing "dangerous goods". The first explosion was equivalent to 3 tonnes of TNT and the second blast 21 tonnes of TNT, it said.

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 specializing in handling "dangerous goods".