Video | Many feared dead in New Zealand mine explosion

Emergency services are racing to the Pike River Coal Processing Plant near the town of Atarau on the west coast of the south island after police received reports of an explosion.

25 to 30 at the mine are still unaccounted for.

Police said workers were in the mine at the time of the blast.

Two rescue helicopters and 10 ambulances were sent to the mine, according to St John Ambulance Service.

The mine's management has said up to 35 workers were underground when the explosion occurred but two miners made it to the surface, saying that they had lost communication with the others.

The mine reaches 1.4 miles underground and produces high-grade coal for export that is used primarily in steel production.

Pike River has been operating since 2008, mining a seam that holds the largest-known deposit of hard coking coal in New Zealand, with 58.5 million tons of coal in-ground, according to its website.

Pike River says its coal preparation plant at the site is the largest and most modern in New Zealand and processes up to 1.5 million tons a year of raw coal.

The mine is not far from the site of one of New Zealand's worst mining disasters - an underground explosion in state-owned Strongman Mine in 1967 killed 19 workers.