Joanna Smorczewska, a spokeswoman for the Gliwice prosecutor's office, told PAP on Monday morning that the proceedings would look into "causing an incident endangering the lives and health of many people... by allowing mining works in an area threatened by the risk of a tremor and methane discharge."

The prosecutors have ordered post-mortems on the bodies of four miners who died in the accident, the spokeswoman said.

Mateusz Morawiecki, the prime minister, announced earlier on Monday two more miners had been confirmed dead.

The Zofiowka mine was hit by a tremor, accompanied by a methane discharge, at 3:40 a.m. on Saturday, some 900 metres underground, forcing dozens of workers to flee the mine. Ten miners, however, were unaccounted for at that time.