Poor weather is hampering work at the Pike River Coal mine on the West Coast.
Twenty-nine workers died following a series of explosions that began on 19 November last year.
Police are eager for more bore holes to be drilled into the mine so they can better assess conditions inside the chamber where the bodies of the men remain.
Superintendent Gary Knowles says the temperature is far from stable and there is still gas underground.
Temperatures have fallen at times as low as 30 degrees Celsius, but risen quickly again by up to another 100 degrees.
Mr Knowles says methane readings are also fluctuating, which is why more bore holes are needed to get an accurate picture of what the atmosphere is like further inside the mine.
However, strong wind gusts and heavy rain have stopped the drilling on Thursday afternoon, but monitoring and the two gas machines are still operating.