Rescuers prepared to drill a gas sampling hole through 500 feet (150 metres) of hard rock and into a New Zealand coal mine where a powerful blast trapped 29 workers nearly two days ago.
Pike River Mine chief executive Peter Whittall told reporters a small six inch (15cm)-wide hole would be drilled into the mine from the mountain above over the next 16 to 24 hours to enable rescuers to sample gas levels from deep in the mine's centre.
Underground combustion that continues to generate dangerous gases was preventing rescuers from entering the mine.
"We've got a heating of some sort underground and that means there's some combustion generating the gases that go with that, carbon monoxide, a slight increase in methane and some other gases," Mr Whitehall said. "Something is happening underground, but what it is we don't know."
The small hole was aimed at an area a couple of hundred metres (660 feet) further into the mine from where the main ventilation shaft is located. "That will give us more information about what's going on" with gas levels near the centre of the mine, he said.
Dangerous methane and carbon monoxide gas levels meant "it's still not safe for rescue teams to enter the mine," Mr Whittall said, though "the oxygen quality coming out of the mine is still high."
Fresh air is still being pumped into the mine through an open air line.
Police search controller, superintendent Gary Knowles, said the "primary focus is still a rescue operation. "Our major focus is bringing these guys home," he told reporters, "but we need a stable air environment. When we have a stable environment ... and as soon as we have that we're going in."
Anguished relatives voiced frustration over the delays in the rescue operation. "If I had my way I'd be down there, I'd go into the mine myself," said Laurie Drew, whose 21-year-old son, Zen, is one of the missing men.
Police said the miners, aged 17 to 62, are believed to be about 1.2 miles (two kilometres) down the main tunnel.