A laser camera inserted into a bore hole at the Pike River coal mine could soon reveal the first images of the spot where miners are thought to be trapped.
Twenty-nine workers are missing inside the mine after an explosion on Friday.
A hole being drilled 162 metres into the ground at the place where the men were working is expected to be completed on Monday. Rescuers then plan to insert laser-imaging equipment into the bore hole.
High gas levels have made it too dangerous for rescue crews to enter the shaft, and rescuers say the need to take air samples once the bore hole is complete means they will not enter the mine on Monday night.
Pike River Coal Mine chief executive Peter Whithall says the last 10 metres of the hole will be bored using a diamond drill bit to avoid sparks that could ignite methane gas inside the mine.
Rescue teams are still waiting to begin their search but officials on Monday said high levels of volatile toxic gases make it too dangerous still to enter the mine.
Rescue workers are also planning to send a Defence Force robot into the mine shaft. Extra cable is coming from an Australian mining company to extend the robot's reach, and it is being modified so it does not give off sparks and cause another explosion.
The Defence Force says the robot, which is used for the disposal of improvised explosive devices, was deployed during the police siege of Napier gunman Jan Molenaar in 2009.
The remote-controlled robot is expected to go into the mine on Monday night after testing by the army. One of the miners who escaped from the explosion, Daniel Rockhouse, says there is enough room for the robot to go right in.
There has been no communication with the miners and contractors at the horizontal mine at Atarau, near Greymouth, since a methane gas explosion cut power and blew out ventilation fans at 3.45pm on Friday.
The men are believed to be trapped about 2km along the Pike River Coal mine tunnel burrowed in rugged mountains and bush and 150 metres below the surface.
Families of the workers have expressed frustration and are anxious for a rescue mission to begin.
Once drillers get through to what they hope will be a space in the mine, they will be able to put fibre optic cable down or a camera and take air samples.
Pike River Coal says the Department of Conservation has agreed to a 2.7km track being cut into the land to allow a walking access to the damaged ventillation shaft.
This will enable more air samples to be taken, and a tube will be put along the length of the track to take air samples directly to a testing site at the mine. The bore hole will also allow rescuers to hear anyone talking.
Testing on Sunday showed the gas levels were generally declining but fluctuating, and there is still a risk of another explosion.
Pike River Coal chairman John Dow said there has definitely been a fire of some sort in the mine, but it is not clear if it is still burning.
The situation is being investigated by analysing gases from the mine. Mr Dow says high levels of carbon monoxide and carbon dioxide are still being found.
Safety paramount, say police
The police officer in charge of the operation has rejected a suggestion that the men's chances of survival are now low.
Superintendent Gary Knowles reiterated it was still a search and rescue operation but he could not risk further lives and the mission would begin only when it was safe.
New Zealand Mines Rescue general manager Trevor Watts says rescuers are ready to go in when the air tests show the smallest window of opportunity.
Mr Watts says it could take about two hours to reach the men by foot once they are given the clearance to begin.
Testing time for families
Families of the workers have expressed frustration and are anxious for a rescue mission to begin.
But officials say high levels of volatile toxic gases means it is still too dangerous to enter the mine.
Prime Minister John Key has spoken with family members and plans to visit the mine on Monday afternoon. Mr Key says it is a testing and difficult time for the families. They are anxious and frustrated, but are aware of the safety issues.
Family members were given another opportunity to head up to the mine site on Monday.
Sixteen of the 29 workers are employed by Pike River Coal, while 13 are local contractors. The youngest of the miners is a 17-year-old New Zealander, while the oldest is 62.
