(CNN) -- The roof of a northeast Idaho mine collapsed Friday, trapping a man inside and setting off a complex rescue operation to save him, the mine's owner and operator said Saturday.
The miner was one of two men working in part of the Lucky Friday Mine when a 10-by-20-foot section of mostly rock fell on him around 5:30 p.m. Friday, according to Phil Baker, president and CEO of the Hecla Mining Co. He added that no more than 75 feet -- out of a 2,200-foot stretch of the mine -- collapsed, with all this happening 6,150 feet below the earth's surface.
While the other man was able to get out unharmed, the trapped miner hasn't been heard from since.
"We're doing everything we can to reach the employee and will continue to make every effort, as long as it takes," said Baker, whose company has owned and operated the mine outside Mullan since 1958. "We are going to bring him out -- that is what we're working toward right now."
Baker, who did not identify the trapped miner, said the cause of the collapse has not been determined. Numerous special bolts and chain-link fence are used to keep the ground above the affected mine in place.
"Our current focus is 100% devoted to rescuing the miner," the mining company executive told reporters. "We will investigate the cause after the rescue efforts are complete."
Hecla employees working in 10-man crews are working around-the-clock on the rescue operation, aided by contractors. Representatives from the federal Mine Safety and Health Administration are also on the scene.
Equipment being flown in from the East Coast to help in the operation is expected to arrive Saturday night, said Mike Dexter, who formerly ran the Lucky Friday mine for Hecla and is now serving as a spokesman.
The man was trapped in a part of the mine where ore is removed and far from either of two possible exits, neither of which was adversely affected by the collapse, according to Baker.
Dexter, who recently retired from his day-to-day job at the Idaho mine, explained that rescue workers won't have to cut through more than 6,000 feet from the surface to get down to the spot where the incident occurred. Rather, they and their equipment take a large shaft 5,900 feet down into the earth, then go north a mile and up a ramp toward the incident site.
Workers had been able to clear out the first slice of ground material -- the roughly 75-foot section that has fallen in -- by Saturday afternoon. But the effort slowed considerably after that because of the challenges in securing the earth and preventing further collapses.
"The first 25 feet came fairly quickly," Dexter said. "Once we had reached that limit ... to where they couldn't go any further, that is where it becomes slow and we have to (stabilize) the roof" of the mine.
Lucky Friday is a "deep underground silver, lead and zinc mine" located in the Coeur d'Alene section of Idaho, near the small town of Mullan, according to Hecla's website. It has been in operation since 1942, according to Dexter.
Hecla has 275 of its employees routinely working at the mine, in addition to about 100 contractors, according to a company statement. Its website describes the Coeur d'Alene-based company, founded in 1891, as the "largest and lowest-cost silver producer" in the United States.
Company officials said there have been no recent collapses or similar incidents at the mine. Baker on Saturday asked for people's "thoughts and prayers" on behalf of the miner, his relatives and those involved in the rescue effort.
"This is a very tough time for the mine, for the Hecla Mining Co. and for all the families associated with this," he said.
CNN's Greg Botelho contributed to this report.