Temperatures and gas levels in the Pike River Coal mine on the West Coat are still fluctuating, police say.
Twenty-nine workers were killed following a series of explosions at the mine which began on 19 November.
A team of police, mines rescue and coal company gas experts continues to work around the clock, trying to make the atmosphere stable enough for recovery teams to enter and retrieve the men's remains.
Police say a GAG machine used to neutralise toxic gases and the Floxal nitrogen generator have been working since Christmas Day, but gas levels are still changeable.
The machines have forced the temperature in the mine down from about 600 degrees celsius during the explosions to about 100 degrees at times.
Last week, police said it would be at least mid-January before any entry of the mine could be attempted and nothing has changed to bring that date closer.