At least five workers have died, and several others were left injured following a blast at a mine in the Asturias region of Spain.

The incident occurred at the Cerredo mine in Degaña, 280 miles northwest of Madrid, on Monday.

A representative of the central government in Asturias, Adriana Lastra, spoke to reporters at the scene.

According to Lastra, initial investigations revealed that the explosion may have been caused by methane forming an explosive mixture in the mine—a phenomenon known as firedamp.

“Police are already investigating what happened; they are already at the scene,” Lastra said.

The injured have been taken to hospitals in nearby cities, two of them by helicopter, suffering from burns and, in one case, a head injury.

Families of the workers have flocked to the site, which was surrounded by police and emergency services vehicles.

Five mine workers killed by explosion in Spain