Emergency services said there was an underground explosion around 4.30pm and there are people known to be in the mine.
Greymouth's emergency services are treating the incident as "highly significant".
Pike River Coal's senior management staff are heading to the scene.
Management is still trying to ascertain what happened and said they have made contact with a person who is inside the mine.
Grey District mayor Tony Kokshoorn is also heading to the mine and said he has been told there are between 25-30 people currently unaccounted for.
"It's too early to make any calls at the moment, but it's not good news at the moment," he said.
The mine runs 2.3km into the earth.
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