Massive explosions have hit China's northern city of Tianjin, leaving at least 17 people dead and hundreds more injured.

State media said the blasts happened in a warehouse storing "dangerous and chemical goods" in the port area of the city.

Pictures and video on social media showed flames lighting up the sky, and buildings are said to have collapsed.

Hospitals are reported to be overwhelmed with casualties.

President Xi Jinping has urged "all-out efforts" to rescue victims and contain the fire, Xinhua state news agency said.

State broadcaster China Central Television (CCTV) said a shipment of explosives had detonated but this was not confirmed.

The first explosion at about 23:30 (15:30 GMT) on Wednesday was followed by another, more powerful blast, seconds later. Shockwaves were felt several kilometres away.

BBC Chinese Service editor Raymond Li says all indications are that it was an industrial accident.

The China Earthquake Networks Centre said the magnitude of the first explosion was the equivalent of detonating three tons of TNT, while the second was the equivalent of 21 tons of the explosive.

Further blasts were subsequently triggered nearby, Xinhua said.

CCTV said four firefighters were among the dead and that more than 400 people had been injured, at least 32 of them critically.

BBC producer Xinyan Yu, who is in Tianjin, said workers' dormitories were among the buildings destroyed.

Source: BBC