A sudden gas outburst in an illegal coal mine in Sichuan Province has left four miners killed and three injured, said local officials on Sunday.

Seven people were in the pit when the accident happened at 11:20 p.m. Friday in Xuanhan County, Dazhou City. Three escaped with injuries, while four others were trapped underground until they were found dead Saturday evening, according to the county's publicity officials.

The three injured are recovering in a local hospital.

Police have detained three people in relation to the accident.

An investigation into the cause of the accident is still underway.