A jet engine, flown to the West Coast of the South Island from Australia, has been running around-the-clock, pumping water vapour down the Pike River Coal mine, in a bid to smother the coal fire.

"At the moment gas is coming up the ventilation shaft and there's still the odd flame licking out of that shaft," Chair of Pike River Coal, John Dow, told Radio New Zealand today.

The Gorniczy Agregat Gasniczy (GAG) unit, from Queensland, was cranked up at the horizontal mine on Wednesday and Mr Dow said the machine would continue to operate for several days before the blaze was out.

"We have atmospheric issues - during the day the air comes one way down the tunnel and during the night it goes the other way," he said.

Start of sidebar. Skip to end of sidebar.

End of sidebar. Return to start of sidebar.

"When the air's coming down the tunnel it's fighting the GAG and so it's not so efficient that time of day.

"The guys think they'll be running it for several days while we evaluate the success."

Once the GAG snuffs out the fire - which is expected to have spread to the coal seam and caused some internal collapse - the machine will blow nitrogen down the shaft to try and cool it down.

This will allow rescue crews to recover the remains of the men who became trapped 2.5km underground when a methane explosion ripped through the coal mine, near Greymouth, on November 19.

"Once the fire's out and once the air coming up the shaft is gases from the GAG machine then we can start putting the lid on the pressure cooker," Mr Dow said.

Another four explosions have happened since the initial blast two weeks ago.

"The flames from last Sunday's explosion set the coal on fire and it was a much darker, much more billowing kind of smoke," Mr Dow said.

"That's evidence of a coal fire and the heat in mine will be retained.

"The GAG engine exhausts themselves are quite hot, so before we can go back underground we've got to wait for everything to cool down."

Mr Dow is confident the Pike River Coal mine will eventually be back in business, but he couldn't say how long it will take to get up and running again.

"Last Sunday, the 25th, when we had the fourth explosion that set the coal on fire, that darkened the outlook significantly," he said.

"It extended the period of time we'd be engaged in this recovery process.

"It's made it a little bit harder, but the board is looking at its options at the moment.

"I don't want to put a time frame on it, but I absolutely believe we can recover the business.

"There's three things we've got to do: We've got to recover our men, we've got to recover our business and we've got to make sure we properly interface with the three inquiries and the royal commission and, of course, our own internal investigation."

As well as a coronial inquiry, the Department of Labour, NZ police and Pike River Coal all had inquiries in the pipeline.

This week, NZ Prime Minister John Key announced a Royal Commission would look at what triggered the blast, how the men died, the rescue efforts that followed and national mining regulation.

A coronial inquiry was also in the pipeline, along with investigations by the Department of Labour and NZ police.

Yesterday, more than 10,000 people attended a national remembrance service near the mountainside mine, paying homage to the 29 men killed in the disaster.