A diamond head drill is being used to bore the final metres of a hole at the Pike River coal mine, to minimise the chance of the drill igniting any methane gas underground when it breaks through.

The hole is being drilled so that gas samples can be taken from the mine, where 29 men remain trapped after an explosion on Friday.

The drilling method was changed to a diamond head drill for the final 10 metres of the 162 metre hole.

"The diamond drilling cuts through rock without causing sparks at the bottom of the hole. It's just a common sense safety procedure," Pike River chairman John Dow said yesterday.

Tasman Area Police Commander Superintendent Gary Knowles told Radio New Zealand the families would be the first to be told once the drill had broken through.

Authorities were briefing the families on the progress of the rescue at 8am before a 10am media conference.

Laurie Drew, the father of missing miner Zen, told Radio New Zealand the families hoped for new developments today, but expected it would "be the same as yesterday".

Mr Drew said he could not understand why relatives were not allowed to stay up at the mine entrance to wait for their loved ones to come out - regardless of the outcome of the rescue.

Grey District Mayor Tony Kokshoorn told TVNZ's Breakfast he felt for the families of the 29 miners who were realistic but not giving up hope.

"It's getting desperate, it has been five days. These families are hanging on to everything they can."

Defence Force robot

Mr Kokshoorn said it was getting close to the point where rescuers should "have a go", and send in the Defence Force's robot.

He said he appreciated the safety of the rescuers should not be compromised but that for the families sake the miners had to be found.

"The robot sounds like a good compromise to me," he said. "[If the robot was sent in] we are going to find out where our miners are."

"It's a new mine. There is a limited area where they can be."

Mr Knowles told Radio New Zealand rescuers had also been offered the use of an American robot that was better suited to entering volatile environments.

At a media conference last night, he said Defence Force staff had been practising with the Defence Force robot all day, testing it on the road to make sure it could handle the terrain inside the mine and go the distance.

He said the robot, also used to detect and dispose of bombs, would have a rag attached to its arm to ascertain if any air was moving in the tunnel. It would have to drag its own fibre-optic cables behind it as it moved into the mine.

Rescuers keeping open mind

Mr Knowles he was keeping an open mind, but admitted planning was under way in the event that any or all of the miners had not survived the explosion or their time underground.

"We are in a major search and rescue planning phase. We still remain optimistic, we're still keeping an open mind, but we're planning for all outcomes," he said.

"Also in part of this process we are planning for the possible loss of life as a result of what is happening underground."

It was still too dangerous for a rescue team to enter the mine, because of the possibility of heating underground, Mr Knowles said.

"Gas analysis teams are now analysing the samples to determine if there is active fire or heating underground that may ignite.

"We need to establish beyond reasonable doubt that an emission source does not exist."

He said a second point was being set up to take gas samples. "I am going to reinforce the fact that we are doing this to ensure the safety of those miners underground and also the teams that have to go and rescue them."

Conditions underground

More details emerged last night about where in the mine the men might be and what conditions they may be experiencing.

Pike River chief executive Peter Whittall said the men would have been deployed to certain areas upon arriving at work. He knew where they had been sent to work within the mine, but could not say for sure if that was where they were.

"We know where the men were deployed to and Daniel Rockhouse has given us a reasonably good account as to where most people were. But we can't definitively say where they are."

Mr Whittall said the men would have all been wearing hard hats that had lamps attached with leads running to a battery they wore on their body. They would also be wearing overalls, steel-capped boots, safety glasses and ear plugs.

"They would have been carrying just what they needed for their shift."

The only food they would have had access to over the past three days - if they could reach the break areas where it was stored - was what they had brought in for their shift. But the mine had several fresh water supplies.

Mr Whittall was reluctant to speculate on what conditions the men might be facing, but he gave some insight into how they might be faring.

He said the miners' cap lamps, if they had been using them all the time, would be flat by now. They only have a 24-hour battery life.

"It will be quite hot ... There's not a lot of ventilation down there."

The mine had a fresh-air change station about 1.8km from the tunnel's entrance, designed to give miners a respite from high gas levels. But a miner had left the airlocked door to the station open, rendering the base useless. The only telephone in the base was also not working.

The trapped miners:
Conrad Adams, 43 (Greymouth), Malcolm Campbell, 25 (Greymouth - Scottish), Glen Cruse, 35 (Cobden), Allan Dixon, 59 (Runanga), Zen Drew, 21 (Greymouth), Christopher Duggan, 31 (Greymouth), Joseph Dunbar, 17 (Greymouth), John Hale, 45 (Ruatapu), Daniel Herk, 36 (Runanga), David Hoggart, 33 (Foxton), Richard Holling, 41 (Blackball), Andrew Hurren, 32 (Greymouth), Jacobus 'Koos' Jonker, 47 (Coben - South African), William Joynson, 49 (Dunollie - Australian), Riki Keane, 28 (Greymouth), Terry Kitchin, 41 (Runanga), Samuel Mackie, 26 (Greymouth), Francis Marden, 42 (Runanga), Michael Monk, 23 (Greymouth), Stuart Mudge, 31 (Runanga), Kane Nieper, 33 (Greymouth), Peter O'Neill, 55 (Runanga), Milton Osborne, 54 (Ngahere), Brendon Palmer, 27 (Cobden), Benjamin Rockhouse, 21 (Greymouth), Peter Rodger, 40 (Greymouth - British), Blair Sims, 28 (Greymouth), Joshua Ufer 25 (Australia), Keith Valli, 62 (Winton).