An explosion in New Zealand's largest coal mine has trapped at least 27 miners underground.

Rescue workers are still waiting to get the okay to begin searching for the men who are believed to be alive somewhere in the mine.

"They're itching to get in there and start looking for other people and a bit frustrated at having to stand and wait," police spokeswoman Barbara Dunn said.

Emergency teams are testing for poisonous gas because the explosion knocked out the power to the ventilation system.

So far, all attempts to contact the miners have been unsuccessful. Five men survived the blast and were able to find their way to the surface.

"We are holding on to hope," Mayor Tony Kokshoorn said. "Look at Chile, all those miners were trapped, and they all came out alive."