A police emergency response unit found four bodies and rescued 10 workers trapped in a collapsed tunnel in Freeport-McMoRan Copper & Gold's Grasberg complex in Tembagapura, Papua, on Wednesday.

Tembagapura Police Chief Adj. Comr. Sudirman told Antara news agency on Wednesday that the 10 rescued workers suffered wounds and bruises from the collapse that occurred at about 7:30 a.m. local time on Tuesday.

"The search effort was carried out from [Tuesday] night to this morning," Sudirman said as quoted by Antara. "It's been temporarily stopped because the [rescue] crew is resting. We're waiting for new crew."

Sudirman said that based on the list of workers given by Freeport, there were more than 40 workers trapped in the tunnel. They were participating in a Quality Management System (QMS) Annual Refresher class, a work safety training, when the tunnel collapsed.

"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." Government authorities had been informed, the company said.

The accident happened outside of areas being mined, about 500 meters from the entrance to the Big Gossan underground mine, Bloomberg reported. It is the biggest incident with the highest number of fatalities in recent years. The mine tunnel previously collapsed in 2003 and killed at least nine workers.

Grasberg in Papua province includes open-pit and underground operations and is the world's third-biggest copper mine ranked by production capacity, according to data compiled by Bloomberg. It also produces gold. Output was disrupted in 2011 and 2012 after labor unrest and violence at the site.

Indonesia accounted for $3.92 billion of revenue last year, or 16 percent of Freeport's sales.

[With additional reporting from Bloomberg and Reuters.]