Police say progress is being made extinguishing the fire in the Pike River Coal mine where 29 men died last month.
They say flames that were coming from the ventilation shaft are no longer visible, and temperatures on the concrete pad around the vent are cooling.
The officer in charge of the recovery operation, Superintendent Gary Knowles, says the disappearance of the flames is an important step towards capping the shaft.
However, he says putting the cap in place depends on workers getting access to the pad, which yesterday reached a temperature of 150°C.
Superintendent Knowles says the cap will make the GAG machine being used to put out the fire more efficient.
Meanwhile, the Chief Coroner was given a full briefing in Greymouth on Tuesday on the recovery operation.
Superintendent Knowles says Judge Neil MacLean was also be taken to the mine site, and will meet the victim's families on Wednesday.
Radio New Zealand understands the cost of running the GAG unit, a modified jet engine, is approximately $10,000 an hour, making the bill already more than $1 million.
The mine's chief executive, Peter Whittall, says because the police contracted the machine, which was borrowed from Queensland Mines Rescue, they have underwritten its cost, but he says no decision has been reached on payment.
Past operations that put out mine fires in Australia and the United States have cost tens of millions and have taken up to a year.