TIMIKA, Indonesia - Rescuers searching for 23 trapped workers at a giant U.S.-owned gold and copper mine in Indonesia spotted six bodies Saturday but weren't able to retrieve them because of falling debris, a company official said.

The collapse at the Big Gossan underground training facility at the PT Freeport Indonesia mine happened Tuesday when 38 workers were undergoing safety training.

Ten miners were rescued and five bodies have been recovered since.

Nurhadi Sabirin, head of the company's emergency response team, said vibrations have been detected that could be a human heartbeat, but they could also have resulted from a number of other causes.

"We have not detected any other potential signs of life in the past 72 hours," Sabirin said. He said rocks falling from above were slowing rescuers.

"We continue to carry out these efforts nonstop, 24 hours a day as quickly as can be done safely to do everything possible to save lives, but as more time passes the possibility of there being any survivors becomes less likely," Sabirin said.

Mining operations at the Grasberg mine in the remote Mimika district in the easternmost province of Papua have been suspended since Tuesday to pay respects to the victims and to concentrate on rescue operations. The company said the accident was expected to have no significant impact on its operations.

About 1,000 workers are blocking a main road about two miles from the accident site in solidarity with the victims, and also to seek a guarantee of safety.

More than 20,000 workers are employed at the mine, owned by Phoenix, Arizona-based Freeport-McMoRan Copper & Gold Inc. The province holds some of the world's largest gold and copper reserves.