Rescue efforts to save the 29 workers have been delayed until the Pike River coal mine is deemed safe enough [AFP]  

Officials in New Zealand have delayed a rescue operation for 29 miners trapped in a coal mine, with police saying they have "no idea" how long it would take to reach the men while expressing hope of finding them alive.

But authorities are preparing to send a high-tech robot down the tunnel on Monday afternoon to transmit images to see if the explosion had blocked the main shaft, and to assess toxic gas levels.

The New Zealand Defence Force robot is being modified to ensure it does not generate sparks as it enters the mine where high levels of flammable methane gas are still being recorded.

Rescuers also hope to send down a camera and laser imaging equipment to look for any sign of the trapped men, and a tube to constantly monitor the air quality.

There has been no contact with the men after an explosion on Friday in the Pike River colliery on the west coast of South Island. Rescue efforts remained on hold on Sunday for fear of another gas explosion.

Authorities say that tests show material is burning in the mine and generating toxic carbon monoxide.

Tense situation

Describing the situation on the ground as tense, Lorelei Mason, a correspondent with TVNZ, said on Sunday that "it could be some time, some days possibly, before a rescue is attempted".

A robot is being modified to safely transmit images from inside the gas-permeated mine tunnel [AFP]

"The latest information we have from the officials is that they are slightly concerned by the level of warmth underground [that] they are detecting ... it could be a fire from coal or gas, or something burning down there," she told Al Jazeera.

The miners, who range in age from a 17-year-old, believed to be on his first shift, to a 62-year-old, include two Australians, two Britons and a South African.

They are thought to be only about 150 metres from the surface but 2.5km from the mine entrance in a tunnel.

"This is not a quick fix. We're into day two. We have no idea how long this will take but we are still focused on bringing these guys out," Gary Knowles, the Tasman district police commander, said on Sunday.

But he denied suggestions that rescue teams were showing a lack of urgency about entering the mine because he appeared to believe the chances of finding the miners alive were low.

"We're talking about people's lives here ... my decision is made based on safety and what [the] experts are saying."

Families concerned

Peter Whittall, Pike River mine's chief executive, said the missing men's families, some of whom have publicly questioned the delay, went to the mine on Sunday to talk to rescuers and gain an understanding of the problems they faced.

However, he conceded that the families' concerns were mounting the longer their loved ones were still underground.
  
"Obviously, it's 36 to 48 hours that have gone by now, they're starting to be very concerned and want as much information as they can," he said.

TVNZ's Mason told Al Jazeera: "Today, we have had extra equipment brought in, new drilling equipment which is going to start work soon, digging a core, six inches wide in diameter, to go down to the tunnel to try and get more testing done [to] allow them to get a better idea of the air quality."

Separately, arrangements were being made to fly relatives of the five foreign nationals among the 29 to New Zealand as the news became  more grim and people packed churches to pray for a miracle.

Source: Al Jazeera and agencies