Blast fears delay search for New Zealand miners

29 men are still missing in the country's biggest underground coal mine, more than 24 hours after a powerful blast tore through the tunnel.

A Red Cross worker stands outside the Red Cross Welfare Centre in Greymouth, New Zealand. Ambulance and emergency crews were on site at the Pike River Coal underground mine.

WELLINGTON, NEW ZEALAND // Rescuers waited today for gas levels and the risk of a second explosion to drop so they could enter New Zealand's biggest underground coal mine to search for 29 men still missing more than 24 hours after a powerful blast tore through the tunnel.

It was not known if the 16 employees and 13 contract miners survived yesterday's explosion. Repeated attempts to contact them have been fruitless, Pike River Mine Ltd's chief executive Peter Whittall said.

"We haven't heard a thing," Whittall said.

A working phone line to the bottom of the mine had rung unanswered. Whittall said one of two men who escaped from the mine had used the phone to contact the surface before walking out.

The two dazed and slightly injured miners stumbled to the surface hours after the blast shot up the mine's 108-metre-long ventilation shaft. Video from the scene showed blackened trees and light smoke billowing from the top of the rugged mountain where the mine is located, near Atarau on New Zealand's South Island.

The blast was most likely caused by coal gas igniting, Whittall said. The extent of damage underground was unknown.

The rescue effort has been delayed by more than 24 hours due to fears that a build-up of dangerous gases could trigger a second underground explosion. The police search controller, superintendent Gary Knowles, said rescuers were ready to go as soon as air quality tests showed low enough gas levels for a safe search.

"We're not going to put 16 men underground and risk their lives," he told reporters.

He remained confident that the missing miners were alive.

"This is a search and rescue operation, and we are going to bring these guys home," Mr Knowles said.

Families of the missing men gathered at a Red Cross hall in nearby Greymouth today, and were being briefed hourly as the rescue drama unfolded.

Anguished relatives voiced frustration as poisonous gases prevented rescuers from entering.

"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.

Air samples taken from the mine were being analysed for traces of methane, carbon monoxide, ethane and other trace gases, and authorities especially wanted to see lowering levels of carbon monoxide, but that had not happened yet, Mr Whittall said.

Mr Whittall said a compressed air line damaged in the explosion was still pumping fresh air into the mine and was "flowing very freely."

"We have kept those compressors going and we are pumping fresh air into the mine somewhere. It is quite conceivable there is a large number of men sitting around the end of that open pipe waiting and wondering why we are taking our time getting to them," Mr Whittall said.

Electricity went out shortly before yesterday's explosion and that failure may have caused ventilation problems and contributed to a buildup of gas. The power outage continued to frustrate efforts today to pump in fresh air and make it safe for rescuers.

The missing miners would have to deal with numerous hazards, including air pollution, high levels of methane and carbon dioxide, and low levels of oxygen, he said. Each miner carried 30 minutes of oxygen, enough to reach oxygen stores in the mine that would allow them to survive for "several days," said the Pike River chairman John Dow.

Australian and British nationals were among the missing men, the New Zealand energy minister Gerry Brownlee said.

Unlike the recent mine accident in Chile where 33 men were rescued from a gold and copper mine after being trapped one-kilometre underground for 69 days, Pike River officials have to worry about the presence of methane, mine safety expert David Feickert said.

He added, however, that the Pike River mine has two exits, while the mine in Chile had only one access shaft that was blocked.