Mining officials and police have conceded they are preparing for the worst, 72 hours after 29 men became trapped in the Pike River coal mine.

In front of a packed media conference last night Superintendent Gary Knowles said 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," the Tasman area police commander 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."

Mr Knowles said he would work through the night planning for all options. "We are doing everything humanly possible to rescue these guys underground. We'll keep pushing on until we have a result. We're not stopping, we're going forward."

The Army yesterday sent a robot to assist with the operation. Pike River chief executive Peter Whittall said if it could operate safely within the main access tunnel, it would be used first to check the area where an underground loader is thought to be blocking access.

Mr Knowles said Defence Force staff had been practising with the 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.

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

Mr 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.

It has been an emotional three days for Mr Whittall, who said earlier he knew all the trapped men personally.

"That was a very difficult list of names for me to stand there and listen to," he said after Mr Knowles read out the miners' names for the first time.

"This is my staff, my friends."

Mr Whittall said he was "very, very proud" of his staff up at the site.