GUWAHATI, India (AP) — An explosion ripped through an illegal coal mine in India’s northeastern state of Meghalaya on Thursday, killing at least 18 workers and injuring another, authorities said.

Police officer Vikash Kumar said rescue teams recovered 18 bodies from the site of the explosion in a remote area of the state’s East Jaintia Hills district. One injured worker was pulled from the mine and taken to a hospital for treatment, he said.

It was not immediately clear how many workers were in the mine at the time of the explosion or what caused the blast.

In India’s east and northeast regions, workers extract coal in hazardous conditions in small “rat hole” mines that are narrow pits in the ground, usually meant for one person to go down. The coal is usually placed in boxes that are hoisted to the surface with pulleys. In some cases, miners carry coal in baskets up on wooden slats flanking the walls of the mines.

The practice is dangerous and largely unregulated, with workers often paid the equivalent of about $18 to $24 for a 10-hour shift.

Meghalaya’s Chief Minister Conrad Sangma said the authorities would track down those responsible for the blast and warned of strict action against illegal mining.

Accidents in illegal coal mines are frequent in India’s northeast region. At least 15 miners were killed after getting trapped in one such mine in Meghalaya state in 2018.