Police have detained three people over an explosion in northwest China's Shaanxi Province which left three others dead, authorities said Saturday.

The blast occurred at the entrance of a gold mine in the province's city of Weinan on June 5. The explosion was caused by illegally manufactured explosives that self-ignited and exploded, said a spokesman with the county government.

Two of the mine's contractors are believed to be among those detained.

The local government received word of the explosion before the investigation started on Wednesday, the spokesman said. The accident was previously covered up.

Rescuers are searching the site of the explosion for more casualties, and further police investigation is under way.