JAKARTA A training tunnel collapsed on Tuesday at the world's second largest copper mine in eastern Indonesia, trapping at least 33 workers underground, the mine's owner, Freeport-McMoRan Copper & Gold Inc, said.
Earlier reports, quoting a mine official at the scene, had said three workers were killed in the accident, but the Arizona-based firm denied any deaths had occurred.
Rescue efforts were under way at the remote Grasberg mine in West Papua province. Output at the mine, which also has the world's largest gold reserves and employs just over 24,000 contract and non-contract workers, was not expected to be significantly affected, the company said.
"A tunnel in the underground training area collapsed, trapping a number of employees," the company said in a statement. "The rescue process is difficult and will take some time to complete."
At least 40 workers had been in an underground training facility when it collapsed early on Tuesday, the statement said. Three people escaped unhurt, while four were rescued and received medical treatment.
"Freeport Indonesia does not expect this event to have a material effect on mining and milling operations or development activities," the statement said.
Government authorities had been informed, the company said.
The collapse is one of a series of worker-related incidents at the mine in recent months.
This month, a group of contract workers returned to work after successful pay talks ended a three-day work stoppage.
The last major strike at Freeport Indonesia, in 2011, lasted for three months, caused copper and gold output to drop 15 percent and was Indonesia's longest-ever industrial dispute.
Freeport Indonesia says its sales are expected to reach 1.1 billion pounds of copper and 1.2 million ounces of gold in 2013, up 54 percent and 31 percent over 2012 figures, respectively, as mining moves into higher ore grades.