URUMQI - A boiler explosion killed four and injured five on early Wednesday morning at a washing detergent plant in Northwest China's Xinjiang Uygur autonomous region.

The explosion occurred at 6:40 am at a plant of the Xiangfei Trading Co in Kashgar city, killing four workers and causing two residential houses to collapse.

Five residents of the homes were injured - one seriously, said an official with the city government.

The injured have been hospitalized, the official said, adding that the investigation of the cause is under way.