A series of inquiries will be launched into the deaths of 29 men at the Pike River coal mine.

Prime Minister John Key tonight announced a Commission of Inquiry into the cause of fatal explosions at the mine north east of Greymouth.

Mr Key said he would be working out the details of the Commission in the coming days.

Energy minister Gerry Brownlee promised to spare no effort in investigating the disaster.

"There will be no holding back on the investigation to find out what went wrong."

The Chief Coroner confirmed he would open a special inquiry on Thursday.

Judge Neil McLean said his inquiries would be designed to help the immediate families of the miners.

It was too early to say whether an inquest would take place, as there would be multiple inquiries over time, he said.

Police Commissioner Howard Broad said his officers were working "round the clock" investigating the tragedy.

He said they had been joined by personnel from the Defence Force, Department of Labour, Ministry of Social Development, Crown lawyers, Treasury officials and politicians.

Labour Minister Kate Wilkinson said the Government had to act quickly to find the cause of the tragedy.

"We've got a lot of questions to ask. We've got to act pretty fast," she told Radio New Zealand.

"There are a whole lot of questions and we want those answers. The families need answers, and we, as a country, need answers."

The Department of Labour said it would carry out an investigation into the Pike River crisis under the Health and Safety in Employment Act.

It would co-operate with the parallel police investigation so both would be completed quickly with minimal "disruption" for witnesses, it said

A Department of Conservation (DOC) spokesperson said the department would cooperate with the Commission of Inquiry. DOC administers the land around the Pike River mine.

* Coroner's inquiries are designed to establish the cause and circumstances of death and to make recommendations on how more deaths in similar circumstances can be prevented.

They can also determine whether the death should be investigated by another authority.

* A Department of Labour statement said Commissions of Inquiry were full independent investigations into matters of major public importance.

Those include "any disaster or accident (whether due to natural causes or otherwise) in which members of the public were killed or injured or were or might have been exposed to risk of death or injury."