The crews had been working underground to stop the fire, but had to be withdrawn after being overcome with the gas, according to reports by the ABC.

The Country Fire Authority said the specialist firefighters needed medical treatment after finding they had higher than normal levels of carbon monoxide in their blood.

Victorian Emergency Services Minister Kim Wells reportedly said that while the men were being cared for, the fire was very challenging to fight.

“We have just got to get that fire out,” he said.

Crews fighting the fire are required to wear personal protection equipment and air-quality monitors, with their blood carbon monoxide levels monitored before going underground, during breaks and the end of the shift, Fire Services Commissioner Craig Lapsley told the ABC.

“The safety of all firefighters is always the highest priority, and operations have temporarily relocated from within the mine, but will continue from the edge,” he reportedly said.

Luc Dietvorst of GDF Suez reportedly said the fire would probably burn for another two weeks.

“It's the coal that's on fire and coal is like a briquette,” he told the ABC.

“You can drop a bucket of water over it. It looks like the fire is out and it will come back as a smouldering fire. So it will take some time before we can really extinguish it.”