An official says at least six workers have been killed and many others remain trapped in a coal mine in the eastern Indian state of Jharkhand.

S.K. Singh, the general manager of the Rajmahal Open Cast Mines, said Friday that the mine collapse took place late Thursday and that heavy smog prevented rescue workers from entering the mine until early Friday morning.

Indian media reports say that as many as 40 workers could be trapped in the mine but Singh said that only 10 mining vehicles entered the mine and company safety rules call for only for one worker per vehicle.