At least 11 coal miners were killed and dozens are missing after an explosion buried parts of a mining complex in Pakistan’s Balochistan province on Thursday, an official said.

Shoaib Nosherwani, Balochistan’s minister for mines and mineral development, told Reuters that 36 people were in the collapsed part of the complex at the time of the explosion.

Of them, 25 were missing late on Thursday night, he said.

Rescue efforts were under way at a depth of 4,000 feet (1,219 meters), said Muhammad Atif, the chief inspector of mines in the province. “We are hopeful to find some miners alive, but chances are low,” he said.

Abdul Ghani Baloch, a senior government mining official in the region, said: “Two mines close to each other were damaged in a powerful methane gas explosion.”

The explosion occurred in Sorange, a remote area near the provincial capital Quetta.