The world's largest man-made excavation - a US copper mine - has been shut down by an enormous landslide that smashed roads and buildings and left two-thirds of the pit base buried.

Nobody was hurt in the collapse at the massive open-cast Bingham Canyon Mine, run by Rio Tinto-owned Kennecott Utah Copper - largely because workers had been evacuated amid several weeks of warning signs the ground was going to shift.

"We started noticing movement in that part of the mine in February," said Rio Tinto-Kennecott spokesman Kyle Bennett, according to The Salt Lake City Tribune.

He said that indications were that the mine’s wall was slipping a millimetre or so each day. The mine monitors for movement at all times.

But, by Wednesday morning (local time) mine engineers started seeing movement of up to 5cm per day and moved out the 37 workers at the bottom of the vast open mine. The company also warned residents nearby that a slide was possible any day.

"At 11am yesterday we moved everyone out, including those who were working in the bottom of the mine," Bennett said. "All of our employees are safe and accounted for."

Bingham Canyon Mine is the largest man-made excavation in the world. It has been in production since 1906, and features a pit almost one kilometre deep and 4km wide.

"This is something that we had anticipated," Bennett told Deseret News.

"We knew the slide was imminent. We had relocated machinery, we had rerouted roads, we had rerouted utilities, we had rerouted buildings."

Ted Himebaugh, Kennecott's general manager of operation readiness, said he had seen nothing like it in his 36 years with the company.

"Our primary goal now is to determine how we can safely resume operations and provide not only the jobs for the people but money to the state of Utah and economy," Himebaugh told Deseret News.

Kennecott is the second largest copper producer in the US, supplying about a quarter of the country's copper, the company's website states.