Cracks around the slimline hole are undermining efforts to control the atmosphere underground.

Despite the good weather, Operation Commander Superintendent Gary Knowles said preparations to attempt to seal the cracks were interrupted over the past two days due to “dramatically rising gas” levels, forcing the evacuation of staff from the hillside of the mine.

"The safety of the people working on the hill is paramount and until we have a clear picture that the environment is stable we cannot begin the sealing work," he said.

The New Zealand Police update yesterday afternoon also revealed the GAG inertisation unit was shut down for scheduled maintenance since Saturday.

The GAG jet engine fired up at 4am local time, according to a police spokesperson this morning.

“Every time the GAG has been turned off the methane just started ticking up again fairly quickly,” the spokesperson told ILN last week.

An Air Liquide nitrogen generator is also onsite, but the portable Floxal inertisation unit is a smaller 500 cubic metre per hour system while the 2000cu.m/h systems are used in Australian longwall mines.