Twelve coal miners were feared dead after a gas explosion at a coal pit in Balochistan on Thursday, officials said.

A local rescue team began the search for the workers in the private mine in Singidi, in Balochistan province, before being joined by two teams from the provincial capital Quetta.

“An accumulation of methane gas caused the blast,” said Abdullah Shawani, the head of the province’s mining department.

“Twelve workers were inside a private mine when the whole mine caved in after an explosion,” added Abdul Ghani Baloch, a senior official in the department.

He said that the rescue teams were slowed down because they could not find the entrance to the mine.

Pakistan’s mines are known to have hazardous working conditions and poor safety standards, and deadly incidents are not uncommon.

Twelve miners were killed in a gas explosion at the same mine in June last year.