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.

State media also said senior managers of Ruihai Logistics, which owned the warehouse where the explosion took place, were being questioned by authorities.

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.