An explosion occurred at the Pike River Coal mine on New Zealand South Island's West Coast on Friday, with 25 to 30 miners unaccounted for, police said.

The incident happened at 04:30 p.m. local time (0330 GMT) in Atarau, which is 50 km northeast of the West Coast town of Greymouth.

Police said that they will not know any detail until officers and ambulance staff arrive at the scene.

Greymouth mayor Tony Kokshoorn,who was on way to the mine, told Radio New Zealand that he has been told between 25 and 30 miners are unaccounted for after the explosion.

Energy Minister Gerry Brownlee said mine officials had no idea what caused the blast, or the condition of the miners who were trapped.

Police, ambulances and helicopters were rushed to the mine.