GUIYANG - Four people were killed and one injured in a slope failure in a phosphate mine in Southwest China's Guizhou province Saturday, local authorities said.

The accident occurred at around 4 pm Saturday in an open-pit mine of Wengfu phosphate mine in the city of Fuquan, killing two people immediately and trapping three others, said the municipal publicity officials.

The three were later pulled out, but two were already dead while one sustained injuries.

An investigation into the cause of the incident is under way.

The mine belongs to Guizhou-based Wengfu (Group) Co, Ltd. which specializes in phosphate mining and compound fertilizer production.

Slope failures can cause casualties and potentially result in a mine catastrophe as unexpected rock movement is often fatal and it can occur with little warning.