Thirteen miners were trapped underground at a South African gold mine on Thursday after an earthquake that measured 2.2 caused a cave-in, mine operator Sibanye-Stillwater said.

The firm said it had made contact with three of the workers trapped in the Masakhane mine west of Johannesburg and had mobilized rescue teams.

“All efforts are being made to locate the 10 employees who remain unaccounted for,” the firm said in a statement.

South Africa is home to the world’s deepest mines.

More than 1,000 mineworkers were rescued after being trapped underground for more than 24 hours after a storm knocked out powerlines supplying electricity to Sibanye-Stillwater’s Beatrix gold mine in February.

Sibanye-Stilwater produces more gold in South Africa than any other company. The company also produces platinum and has operations in the United States.