Four workers have been pulled alive from a tunnel that caved in at Freeport McMoran's Grasberg gold and copper mine in Indonesia's Papua province.
But the local police say about 30 people are still trapped underground and they don't know what condition they are in.
The mine is high in the mountains of Papua province.
Freeport-McMoRan says the rescue operation is difficult and will take some time.
The company did not disclose the nationalities of those trapped, although the vast majority of the more than 24,000 workers at the mine are Indonesian.
Neither police nor Freeport have said why the accident happened.