New Zealand 'needs answers' on mine disaster: PM

"We need answers to what happened at Pike River, clearly something's gone terribly wrong and it's now claimed the lives of 29 people," Key told TVNZ.

Key said the nation was in mourning for the miners at the Pike River colliery, who were trapped by an explosion last Friday and confirmed dead after a massive second blast rocked the mine yesterday.

"We owe it to their families and we owe it to New Zealand to give them the answers of what actually took place," said the prime minister, who will visit grieving families in the town of Greymouth later today.

Key praised the stuttering rescue efforts at the mine, which have been criticised by some grieving relatives after the threat of poison gases in the mine stopped rescuers going underground.

"It wasn't for the want of trying, or the willingness, or the courage or the bravery of those that would have gone in to undertake the rescue, it was just the reality of the situation," he told Radio New Zealand.

"A mine in this condition is a highly volatile environment, liable to explode at any time without any notice." Authorities have launched at least four enquiries into the disaster, whose victims ranged from a 17-year-old on his first shift to a 62-year-old veteran, and included two Australians, two Britons and a South African.