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An explosion has rocked a remote colliery in New Zealand, trapping 29 miners underground, the company and local authorities say.

The explosion took place in the Pike River Coal Processing Plant in Atarauon on the west coast of South Island at 4:30pm local time (0330 GMT) on Friday.

Stephen Parker, a TV3 reporter in Wellington, the capital, told Al Jazeera that up to five miners had emerged safely.

"It appears two miners were led to safety and there are reports that an additional three miners have emerged as well," he said.

"However they were working in an area away from the blast. Two of them have been taken to hospital and are being treated for minor injuries."

'Considerable force'

Parker said one of the main concerns is that the ventilation shaft at the entrance to the mine is reportedly covered in black soot.

"It suggests there was quite a considerable force in this explosion and emergency services have expressed concern about the lack of power needed to pump fresh air into the mine," he said.

"There have been reports of emergency rescue teams arriving with ventilation equipment. The situation looks grim and there has been no communication with the trapped men."

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

One mine safety expert said the blast could have been a gas explosion.

"There are different kinds of explosions that can occur in a coal mine - methane gas, coal gas and so on,'' he said.

"If rescue teams can go in, that's good news indeed."

Pike River Coal's office in Wellington said they were still working out what had taken place.

Peter Whittall, chief executive of the company, said he was not aware of any deaths caused by the blast.

He said the men who escaped the explosion were being interviewed and they were "trying to determine ... the full nature of the incident."

Rescuers waiting

Whittall said 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,'' he said.

"They will work throughout the night and they'll work until they can go right throughout the mine and determine the extent of the incident and the safety of our employees.''

Rescue crews were assembling at the opening of the mine but had not yet entered.

The St John Ambulance service said three rescue helicopters and six ambulances had headed to the mine.

The police area commander said details were still sparse but initial reports suggested those still in the mine could be up to 1,500m underground.

Gerry Brownlee, the New Zealand energy minister, said emergency exit tunnels were built into the mine but that he did not know if they could be accessed by the miners.

Source: Al Jazeera and agencies