Three rescuers have been killed while searching for the six miners missing since 6 August in the US state of Utah.
Six other rescuers are being treated after sustaining injuries in the cave-in, which may cause the scale of the rescue operation to be reconsidered.
The mine is located around 193km southeast of Salt Lake City and it is understood the latest accident was caused by a 'seismic bump' which can occur when pressure bearing down on a mine forces a tunnel's roof or walls to cave in.
The accident came on the 11th day of the operation to locate the six miners, who were buried 450m in the original incident.
Rescuers, all colleagues of the missing men, have been digging slowly towards the chamber where the miners were believed to be working.
Three bore holes have been drilled into the area of the mine where the missing men are believed to be, but have so far detected no sign of life.
There has been no contact with the missing men since the accident, although officials have refused to give up hope of finding them alive.
