An explosion occurred at the Pike River Coal mine on New Zealand South Island's West Coast on Friday afternoon, with up to 27 miners remaining inside unaccounted for, police and media reports said.

The incident happened at 4.30 p.m. (03: 30 GMT) in Atarau, which is 50 km northeast of the West Coast town of Greymouth.

At least two people have now emerged from the mine, following the explosion. They have been taken to Westport DHB with moderate injuries.

The two miners indicated three of their colleagues were also on their way to the surface.

Pike River Coal Mine said communication was lost with the 27 following the explosion late on Friday afternoon. Police said there are no reports of fatalities.

Tasman Police communications manager Barbara Dunn said an electrician went into the mine just before 4 p.m. to investigate a power outage and found a loader driver who had been blown off his machine about 1500 meters into the mine shaft.

Dunn said the loader driver and another miner made their own way out. They have moderate injuries and have been taken to Grey Base Hospital.

Dunn said they indicated three others were on their way to the surface, Radio New Zealand reported.

There is no indication yet of the cause of the blast.

Pike River chief executive Peter Whittall told Radio New Zealand earlier in the night one miner who reached the surface confirmed an explosion had occurred.

Grey District Mayor Tony Kokshoorn, who has gone to the mine, said police told him the situation is very serious.

Six ambulances and three fire trucks are at the mine. Three rescue helicopters from Nelson, Greymouth and Christchurch were also dispatched.

Pike River Coal Processing Plant is in the Paparoa Ranges 50 km northeast of Greymouth. The mine entrance is about 2.3 km long and then branches into sub areas.

It holds the largest-known deposit of hard coking coal in New Zealand, with 58.5 million tonnes of coal in-ground.

The company had recently almost halved its production forecasts for the 2011 year to between 320,000 and 360,000 tonnes.