It could take weeks for a GAG unit to put out a coal fire in the Pike River mine, police say.

It is hoped that the GAG (Gorniczy Agregat Gasniczy) machine will put out the fires with the use of water vapour so teams can attempt to retrieve the bodies of the 29 men from the West Coast mine.

The unit has been operating overnight and is expected to have to keep working through the weekend, Superintendent Gary Knowles says.

"We're likely to be talking weeks rather than hours or days.The results so far are positive but this will be a long process," he said.

The machine began pumping CO2 into the mine on Wednesday night, and police said today the fire was being gradually suppressed.

Sampling and analysis of gas levels and temperatures in the mine are continuing at Pike River.

"Once the GAG unit has suppressed the fire the mine will then be filled with nitrogen to create an inert atmosphere. We are continuing to work towards a recovery operation but can't consider sending teams in until we're sure it is safe to do so."

Australian mines experts David Cliff is expected to front a briefing on the progress of the "GAG" unit later today.

Mine will run again, Pike River management says

Meanwhile, Pike River management says it's confident of getting the mine up and running again.

The West Coast mine shut down on November 19 after an explosion, which left 29 miners and contractors trapped. A second explosion five days later dashed any remaining hopes of finding the missing men alive.

Speaking the day after thousands of mourners gathered for a remembrance service in Greymouth, Pike River Coal chairman John Dow said getting the mine working again was definitely feasible.

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

"I've been saying to the team here 'there are three things we've got to do'. We've got recover our men, we've got to recover our business, then we've got to make sure we properly interface with the three inquiries."

Mr Dow said concern for the mine's future had increased as the severity of the situation became clearer, when third and fourth explosions rocked the site.

"After the first explosion on November 19, we thought the problem of recovering the ground would be putting out a gas fire.

"Last Sunday 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 that we'd be engaged in this recovery process, and time works against you when the money clock is ticking."

Mr Dow said all the mine's workers remained on the payroll, but some contractors had lost jobs.

"We've given force majeure notices to the coal freight people, we're obviously not sending any coal out," he said.

"We'll be talking to other goods and service suppliers next week and coming to some kind of understanding with them about what happens next."

Mr Dow said the company was not under pressure from banks, and it had renegotiated a 90-day standstill period on loan agreements following the first explosion.

The jet-propelled GAG machine brought in from Australia to help extinguish the fires burning in the mine was working well, Mr Dow said.

It was not clear how long the machine would need to be used for, although it was likely to be several days yet.

Once that air was stabilised, work would begin to cool the mine to allow recovery teams to retrieve the men's bodies.