The effort to put out the fire burning in the Pike River Coal mine will continue throughout Friday night as more cooling gases are pumped into the tunnel.
A converted jet engine brought over from Australia has been operating continuously for 36 hours and mines recovery teams say it is working well.
A mine scientist from the University of Queensland, David Cliff, says the unit has pumped a large volume of gas into the mine, but it will take a great deal more to put out the fire.
Dr Cliff says the mine is the most challenging he has come across in terms of its location and the difficulty in sinking bore holes.
He says he has never been to a mine that presents so many natural difficulties. Capping the shaft could be done by crane in Australia, but at Pike River it will have to be done by helicopter, and helicopters cannot hover over a fire or thermal draft.
Dr Cliff says it is hard to get accurate information on gas levels in the mine, because sinking more bore holes to check the levels is fraught with difficulty in the mountainous terrain.
Police say the operation will take weeks rather than days, and the jet engine will run throughout the weekend.