Construction, Forestry, Mining and Energy Union district vice-president Greg Sharp said the 55 or so men who were underground when the fire began were "incredibly lucky to get out as they did".

District check inspector Keith Shaw - the Hunter's most senior union safety figure - said gas monitoring devices were still showing combustible gases coming from the fire area and it could be a week to 10 days before the fire was out.

"One bloke said he saw flames behind the longwall face at the tailgate side of the longwall," Mr Shaw said.

"It was an ignition of methane but until we get in there to have a closer look the rest of it is conjecture."

Union district president Peter Jordan said rumours the fire had been started by a lightning strike hitting a gas vent appeared to have been discounted.

It could be some time before Blakefield operated again and the union was working with operator Xstrata to see if men could be moved to other Xstrata mines.

Mr Sharp said union officials would meet with Xstrata at Blakefield on Friday with a mass meeting of Xstrata Blakefield workers to be held on Monday.

"The company has kept the permanent and casual workforce on pay but things are not looking so good for the contract workers," Mr Sharp said.

Xstrata spokesman James Rickards said Blakefield South employed about 550 people.

Mr Sharp said about 220 were union members, another 70 or 80 were staff or mine deputies and the rest would be contractors.