Three rescuers have died and six have been injured during efforts to reach a group of coal miners trapped underground in the US state of Utah.
It is thought that the rescue workers were caught in a cave-in as they tried to dig a tunnel to the spot where it is believed the six miners are trapped.
It remains unclear whether below-ground rescue efforts will continue.
No contact has been made with the trapped miners since a tunnel collapsed 1,500ft (457m) underground on 6 August.
Utah Governor Jon Huntsman called on Friday for underground search operations to be suspended unless workers' safety could be absolutely guaranteed.
"We as a state don't want any more injuries. We've had enough," he told a news conference.
Above-ground drilling efforts to locate the six missing miners are reportedly continuing, with a fourth hole aimed at a spot where "noise" was picked up by a listening device on Wednesday.
Although that development raised hopes, experts say the chances of finding the miners alive are now slim.
'Mountain bump'
Since the first mine collapse, rescue teams had tunnelled about 250m towards the trapped miners, with about 350m to go, when the latest accident happened at 1835 (0035 GMT) on Thursday.
Dirk Fillpot, spokesman for the federal Mine Safety and Health Administration, said the collapse was caused by a "mountain bump" - a build-up of pressure inside a mine from overhead rock that forces surrounding rock and coal to shoot out of the walls with great force.
"It just feels like a really hard blow to swallow after all we've been through the last week and a half and everyone trying to cope"
Efforts to reach the trapped men have also been severely hampered by frequent seismic movement inside the mountain, which has caused the walls of the mine to collapse on several occasions.
On Wednesday, a seismic jolt caused one of the mine's supports to burst, partly burying a machine being used to clear the shaft.
Mr Fillpot said all rescue workers had now been evacuated from the mine. Some 130 people, many of them colleagues of the missing miners, had been involved in the operation.
Huntington Mayor Hilary Gordon told TV news network CNN on Friday: "It just feels like a really hard blow to swallow after all we've been through the last week and a half and everyone trying to cope in their individual way."
Initially the original collapse was blamed on an earthquake, but experts have since suggested the shafts might have caved in with enough force to register on seismographs.
This has led to speculation that mining procedures could have triggered the incident.
The workers may have been using a technique known as "retreat mining", where the last standing pillars of coal are pulled down and the roof is allowed to fall in.
The mine's owners have repeatedly insisted their operation was safe and that the mine collapse followed a natural earthquake.
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