At least two people are dead and 30 injured after an explosion in the Chinese port city of Ningbo.

The explosion was at a factory in a district on the Yong River at about 8.55am on Sunday, according to the official Xinhua News Agency.

Windows were shattered and walls of buildings up to a kilometre away had holes left in them by the blast, the agency added.

Debris was scattered for dozens of metres.

Nearby residential buildings were knocked down, said Huanqiu.com.

These buildings had been empty and were set to be demolished, although there may have been people in the area collecting scrap materials for recycling.

Rescue efforts are continuing.

The cause of the blast is unclear, although the state broadcaster denied it was due to a gas explosion.

Ningbo is around 60 miles south of Shanghai.