The level of toxic gas in the Pike River mine remains too high after last Friday's blast for rescue teams to be sent in to find 29 trapped miners, authorities said this morning.

Tasman Area Police Commander Superintendent Gary Knowles told a media conference he could understand that relatives were extremely frustrated but that safety was "paramount".

"Experts still tell us that the levels of toxicity in the air underground are still too unstable to send rescue teams in," Mr Knowles said.

Tests still show there is also some combustion in the mine.

"We are depending on experts and we will not go underground until the environment is safe."

Mr Knowles said a member of the team drilling a bore hole into the mine so that gas samples could be taken had been injured overnight. It was initially thought he had broken his leg but the injury turned out to be a sprain.

"These guys are working 24 hours a day," he said.

The bore hole will allow cameras and listening equipment to be lowered into the mine shaft and enable scientists to take regular air samples.

Mr Knowles said overnight seismic equipment had been attached to tubes at the mouth of the tunnel.

He said the device would detect any movement - such as tapping - from the mine but could not record voices.

Second bore hole planned

Pike River CEO Peter Whittall said three minutes before the media conference the bore hole was at 142 metres and it was estimated that it would be another five hours before drilling was completed [approximately 3.30pm].

Mr Whittall said a second bore hole - close to where the men were thought to have been working when the blast took place - was also planned.

"We have not started that hole yet, there is not a drill rig on that site yet.

"If the air is heavily concentrated in this first hole, this [second] hole may not give us a lot more information from a gas point of view," he said.

He said they were also looking at further bore holes.

"We know where we want them we just can't get them there. This is extremely difficult topography."

Mr Whittall said "combustion" in the mine was also preventing rescuers entering the mine.

He said this morning's briefing was very difficult for the missing miners' families.

"They are under a lot of stress, they are really struggling. Some of them are coping better than others."

Rescuers 'ready to go'

Trevor Watts, general manager of New Zealand Mines Rescue, told the conference everything was "ready to go" for a rescue, with 65 underground mine rescue staff and 30 logistical support staff.

But he said expert analysis on the "explosibility" of gas in the mine meant his team could not enter the mine.

"I can't express the frustration our guys feel at not being able to deploy underground. It is heart-wrenching."

He warned against comparisons between NZ Mines Rescue and the Fire Service, who he said worked in "horrendous conditions" but normally had windows and doors within a few metres.

"In an underground coal mine our teams will be working up to 3km from safety," he said.

'We have to be honest'

Mr Knowles said rescue teams were still planning for all possible outcomes.

"I'm a realist. We're now into day three. With the passage of time we're preparing for all options. It may include a rescue or it may include a recovery option.

"We still remain optimistic overall but we have to be honest," he said.

"We are looking at what happened on the day, what has happened since then, what the conditions are like, and what are the chances of survival.

"If one of those options means those guys are underground and are not alive, we are planning for that as well."

There will be another family briefing at 4.30pm followed by a 5.30pm media conference.

Robot stalled

Earlier, relatives were told that a Defence Force robot had been sent into the mine but had not been waterproofed and malfunctioned when water fell onto it.

Mr Knowles told media that rescuers were trying to get more advanced robots from colleagues in Western Australia and America to deploy underground.

He said the Royal New Zealand Air Force would fly in the robots on a Hercules aircraft.

Grey District Mayor Tony Kokshoorn said the breakdown of the robot had was a "kick in the guts" for family members and made them question the rescue efforts at Pike River.

"People really started to be questioning of the procedures. There's a certain amount of anger coming up now. It was very emotional for everyone including myself."

Frustration turned to anger when family members after they were told a replacement robot was being flown in from the United States, he said.

Diamond head drill

A diamond head drill was today being used to bore the final metres of a hole at the mine, progress is being slowed by hard rock in the last 20 metres.

The drilling method was changed to a diamond head drill for the final part of the 162 metre hole to minimise the chance of the drill igniting any methane gas underground when it breaks through.

Mr Knowles told Radio New Zealand the families would be the first to be told once the drill had broken through.

Laurie Drew, the father of missing miner Zen, told the broadcaster 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.

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).