Families of workers killed at the Pike River Coal mine have been shown a video with flames and debris shooting from openings in the mine.
The 29 men were killed after explosions began at the West Coast mine near Greymouth on 19 November.
Grey District mayor Tony Kokshoorn says the families were very subdued as they watched the video on Monday which showed large flames shooting up a ventilation shaft.
Mr Kokshoorn says families are now beginning to give up hope of having their loved ones returned to them.
Police have refused to publicly give any information on how the operation went on Monday.
A fire is continuing to burn at the mine, but neither police nor the company is saying what that means for recovery efforts.
There have been four explosions since 19 November - the latest occurring on Sunday about 2pm that sent out coal smoke and flames, rather than gas.
Pike River Coal bosses say it is likely that coal brought down by the explosions is on fire.
Experts have been discussing options with the company which include sealing the mine, at least temporarily, to put out the fire.
Pike River mine entry may take 'weeks'
The manager overseeing a jet engine to be used to extinguish the smouldering fire says it could be weeks or months before people are able to go into the mine.
The GAG machine, which can pump inert gases into the mine site to stabilise the volatile environment, is being set up at the mine.
New South Wales Mine Rescue Service general manager Paul Healey told Morning Report the machine would need to operate for days, but it will take longer for the site to cool down after that.
He says there is a danger of the fire re-igniting if the site is not sealed properly.
Open cast mining 'never an option'
Pike River Coal chief executive Peter Whittall says open-casting mining at the site was never feasible because of the depth of the coal seam and the terrain.
It has been suggested that if Pike River had been an open-cast mine, the lives of miners would not have been at risk.
Mr Whittall says the seams are between 110 and 700 metres below the surface, because the size of the mountains above the seam changes.
Even if the mine was not under conservation land, he says, engineering issues would rule out an open-cast operation.
