JAKARTA (Reuters) - At least three people were killed on Tuesday and an unknown number missing after a training tunnel collapsed at the Indonesian unit of Freeport-McMoRan Copper & Gold Inc (FCX.N), mine officials said.
Output at the world's second-largest copper mine was not expected to be significantly affected, they said.
Freeport Indonesia operates the Grasberg mine in West Papua province, which also has the world's largest gold reserves and employs just over 24,000 contract and non-contract workers.
An emergency response and safety team were conducting a search and rescue, Freeport said in a statement.
"A tunnel in the underground training area collapsed trapping a number of employees," the company said in the statement. "The rescue process is difficult and will take some time to complete.
"Our thoughts and prayers are with our fellow employees and their families as we proceed with rescue efforts."
Several officials at the mine, who were not authorised to speak to the media, said three people had been killed and at least 30 people were missing, but that was not confirmed by Freeport.
"We cannot confirm the number of injured or trapped individuals nor whether there have been any fatalities," the Arizona-based firm said in a statement.
"Freeport Indonesia does not expect this event to have a material effect on mining and milling operations or development activities."
Government authorities had been informed, the company said.
The collapsed tunnel 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.
(Reporting by Sam Wanda in Timika in West Papua and Michael Taylor and Randy Fabi in Jakarta; Editing by xxxx)