Pike River mine on fire

People working near the entrance to the mine were moved away from the area for their safety. Photo / Simon Baker

Large amounts of smoke and flames are coming from the Pike River Coal mine after a fourth, powerful explosion today and boss Peter Whittall says it may have to be temporarily sealed.

"There is quite a large amount of smoke coming out of the mine. This smoke has changed, it's no longer a gas fire, it's obviously now a coal fire," chief executive Mr Whittall told a press conference at 7pm. Families were told of the news at 5pm.

"Where that coal fire is or how big it is, we don't know."

The worst-case scenario is that the actual coal seam would start to burn. A gas fire was pretty easy to put out, but a coal fire in a seam would be a "very different beast", he said.

Operators were still hoping to deploy the Gorniczy Agregat Gasniczy (GAG) jet engine to deploy inert gases and smother the fire, but were now having to consider temporarily sealing the mine, to starve it of oxygen.

However, this was not the preferred option, he said.

The risk assessment team members were still considering the best option.

"We've had a lot of explosions underground, so we've obviously dislodged a lot of coal so there's (been) a lot of fuel in the mine to burn."

Mr Whittall told reporters he thought today's explosion, at 1.55pm, would have been stronger than the previous three. Unlike the previous ones, it went straight up the mine shaft "quite violently", rather than out the entrance tunnel.

It was the fourth explosion in the mine since a blast on November 19 trapped 29 men in the mine, and another blast on Wednesday dashed any hopes that they might be found alive.

Mr Whittall would not comment on the attempts by a robot to enter the mine, its likely state or how the bodies of the 29 men would be recovered.

However, Inspector Mark Harrison said that the bodies may no longer be "intact".

There were no injuries from today's explosion and people working near the entrance to the mine were moved away from the area for their safety.

Superintendent Dave Cliff said the latest explosion demonstrated the volatility of the environment surrounding the mine.

"Our focus continues to be on the safety of those people working at the mine site and the recovery team.

"We are doing all we can to progress the recovery operation, however the explosion reinforces the risks involved in working in this environment and the requirement to put people's safety first."

- NZPA