The 10cm high flame was found after workers on the face smelled smoke.

The longwall had been stationary for 24 hours due to strata issues at the mine, with 5m of structure having been removed and the boot end raised to full height for clearance.

This caused material to spall from the off-walk side rib under the belt.

As the boot end lowered over time due to hydraulic cylinders creeping, the belt ended up making contract with the spalled material.

The NSW Resources Regulator said when defects were found on equipment, additional controls should be put in place until repairs could be done.

It said mine operators should also check all conveyor equipment and carry out strata inspections of the off-walk side of conveyors.