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

With 29 men trapped in a coal mine on New Zealand's South Island set to spend a second night underground, Australia has offered its support for the rescue effort.

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The mountainous area is cordoned off - but rescue operations for the 29 missing men remain on hold

Kevin Rudd, Australia's foreign minister, said on Saturday that his government was sending a technical expert and a rescue team of six, according to ONE News, a New Zealand TV news programme.

"We will be working very closely with the Kiwis," he said.

There has been no communication with the miners since an explosion rocked the Pike River colliery - the country's largest coal producer - near Greymouth on New Zealand's west coast on Friday. It is not known whether the men are dead or alive.

Air samples taken on Saturday at the coal mine to determine safe levels for rescue crews showed that gas levels were too high for any immediate rescue attempt.

"As the search commander I am not prepared to put people underground until we can prove it is a safe environment," Gary Knowles, police superintendent, said. "We still remain positive and we believe that once that window of opportunity opens, we are ready to go."

Trapped gas

The biggest impediment to the rescue is a mixture of methane and oxygen gas trapped inside the mine, suggesting that a second coal-gas explosion is likely, Hamish Clark from TV3 News New Zealand told Al Jazeera.

"The problem that they've got is that they can't get the gas moving through the shaft," he said. "There's no power to the mine itself, which is two and a half kilometres inside the hill."

Poor weather was also hampering access to the ventilation shafts.

Video from the scene showed blackened trees and light smoke billowing from the top of the rugged mountain in Greymouth where the mine was.

David Feickert, a mine-safety expert, cautioned that "there could be another explosion", saying that mine officials had to worry about the presence of methane, unlike the accident last month at a gold and copper mine in Chile where 33 men were rescued alive after being trapped for 69 days.

Feickert said the Pike River mine had two exits, unlike the Chile mine which had only one access shaft that was blocked.

New Zealand police announced the nationalities of the trapped miners on Saturday. There are 24 New Zealanders, two British citizens, two Australians and one South African.

Three New Zealander have been publically identified so far - Milton Osborne, a Greymouth district councillor, Blair Sims and Ben Rockhouse.

One of the Australians has been named as Josh Ufer.

Of the 29 trapped miners, 16 are full-time employees and 13 are contractors, aged between 17 to 62.

Peter Whittall, the chief executive of Pike River mine, said the missing miners would have to deal with such hazards as air pollution, high levels of methane and carbon dioxide, and low levels of oxygen.

He said earlier that the horizontal mine tunnel would make the rescue effort easier than if the shaft was at a steep angle.

"We're not a deep-shafted mine, so men and rescue teams can get in and out quite effectively, and they'll be able to explore the mine quite quickly," Whittall said.

Drinking water

The Pike River coal mine is about 2.3km long, with the trapped men believed to be most of the way inside.

There are a number of ventilation shafts which climb vertically at least 100 metres to the surface to provide fresh air.

Authorities say the miners should have enough access to natural drinking water inside the mine.

Each man was equipped with 30 minutes of oxygen - enough to reach vents or containment rooms with a few days worth of breathable air.

Police said the electricity in the mine went out shortly before the blast which may have caused ventilation problems.

The St John Ambulance service said three rescue helicopters and six ambulances have been despatched to the mine.

Source: Al Jazeera and agencies