At least 21 people were killed and five others injured, three seriously, after a pipe explosion hit a power plant in central China's Hubei Province Thursday, local authorities said.

A high-pressure steam pipe exploded at the Madian Gangue Power Generation Co. Ltd. in Dangyang City around 3:20 p.m.. The injured have been rushed to hospital, according to local authorities.

The cause of the blast was not immediately known.

Rescue efforts are underway.