Murray has insisted a magnitude-3.9 earthquake caused the mine collapse, and has said at least 10 "aftershocks" have been recorded, with seismic activity earlier wiping out more than 300 feet of progress and halting rescue efforts temporarily.

CNN: Camera lowered into mine cavity shows 'survivable space'

Emergency services in western Poland have rescued 19 miners who were trapped underground when a minor earthquake caused a tunnel to collapse.

BBC: Poland miners: 19 rescued after earthquake