A 20-tonne nitrogen generator is now pumping nitrogren into the Pike River Mine.

Police say the Floxal nitrogen generator has been installed and began operating at 6.15pm.

It is hoped the nitrogen will reduce the temperatures within the mine.

The machine had been trucked to Greymouth after landing in Auckland yesterday afternoon and arrived at the mine around 1.30pm.

Work has now begun to unload the machine and prepare it for operation but it is not yet known when the machine will begin pumping nitrogen into the mine.

It is hoped the nitrogen will help cool the environment inside the mine.

Pike River chief executive told 3 News: "We can't really get men underground while the GAG is running. Whereas ... they could go in while the Floxal is running."

Meanwhile, the GAG machine continues to pump water vapour into the mine to maintain a stable environment and preparations are under way to complete the next bore hole.

Grey District Mayor Tony Kokshoorn said it could be some time, however, before recovery teams are able to enter.

"They are talking possibly up to three months," he told 3 News.