An operation has begun to extinguish a fire coming from the vent shaft of the Pike River Mine and cool the concrete pad that surrounds it.
Twenty-nine men died in the mine in a explosions that began on 19 November.
Superintendent Gary Knowles says emergency staff who are working to recover the bodies need to access the concrete pad to assess capping the vent.
Temperatures on the pad are reaching 150°C, and firefighters can't work on it safely when the temperature exceeds 65°C.
Water is being pumped from a creek to a holding tank above the vent and will be used to douse the vent and pad.
A metal cap has been built, and will be lowered by helicopter once the flames and heat reduce.
Superintendent Knowles says capping the vent will make the GAG unit, the modified jet engine being used to neutralise the gases inside the mine, more efficient but says it won't reduce the intensity of the fire inside the mine.
Water will be used to cool it and the surrounding concrete pad.
Superintendent Gary Knowles says they must get access to the pad to further assess capping the vent, which will increase the efficiency of the GAG unit.
A metal cap will be lowered by helicopter over the vent once it's safe to do so.
GAG machine operating well
Police say the GAG unit continues to work well after it was restarted at lunchtime on Sunday following the replacement of two high pressured water hoses.
Before the breakdown on Sunday, the GAG machine had been operating continuously since 10pm on Wednesday, pumping carbon dioxide into the mine.
Engineers have replaced two high pressure water hoses and carried out extensive maintenance.
The hoses were sent to Christchurch for engineers to fabricate exact copies.
Police say the portal has been further sealed while the machine was shut down which will increase its efficiency.