26 November 2010 Last updated at 03:28 ET

Third blast hits New Zealand mine

No-one was near the mine entrance when the third blast happened, officials said

A third explosion has hit a New Zealand coal mine almost exactly a week after an initial blast trapped 29 miners.

Hopes of finding any survivors were dashed by a second huge explosion at the Pike River mine on Wednesday.

No-one was injured in the latest blast at the mine, which is filled with volatile gases.

Prime Minister John Key has warned it may take months to recover the men's bodies, and pledged an investigation, saying the nation "needs answers".

The latest blast happened at 1539 local time - almost exactly one week since the initial blast that caught the men - 24 New Zealanders, two Australians, two Britons and a South African.

The third blast was less powerful than the earlier two, and no-one was near the mine entrance when it happened, said Pike River Coal chairman John Dow.

New Zealand mine disasters

1879: Probable gas explosion kills 34 men and boys at Kaitangata mine

1896: Suspected gas explosion kills 65 men at Brunner mine, near Greymouth

1914: Gas explosion kills 43 men at Ralph's mine in Huntly

1926: Explosion kills nine men at Dobson mine, near Greymouth

1939: Carbon monoxide asphyxiates 11 men at Glen Afton mine in Huntly

1967: Gas explosion kills 19 miners at Strongman mine, near Greymouth

2010: Explosions at Pike River mine, near Greymouth, are believed to have killed 29 miners

The explosion would not affect attempts to recover the bodies, he said.

"We've consistently said that this is a potentially explosive environment. The plans we have in place will continue because we've expected this," said Mr Dow.

Emergency workers have been unable to enter the mine because of high levels of combustible gases, plus a suspected fire deep underground that could ignite them.

Pike River chief executive Peter Whittall said a jet engine that could blow inert gas into the mine had arrived from Australia and would be transported to the mine.

The machine can pump carbon dioxide, nitrogen gas and water vapour into the mine's tunnels to expel oxygen that could fuel more explosions.

Workers could then enter the mine.

Speaking in Greymouth on the South Island on Thursday, the prime minister promised an investigation into the accident.

Mr Key said an independent commission of inquiry would "leave no stone unturned".

The recovery operation could only take place "in a way that is safe to those that would undertake that mission", he said, adding that international experience showed this could take months.

The board of Pike River Coal was expected to meet on Friday to discuss the future of the mine - seen as an economic lifeline for the region when it opened in 2008.

Analysts say New Zealand's mines have a good safety record, and this was the worst disaster for almost a century.

• New Zealand's largest coal mine
• Employs some 150 people
• Operational since 2008
• Accesses Brunner and Paparoa coal seams via 2.3km tunnel under Paparoa Ranges
• 5.5m-wide, 4.5m-high tunnel bisects Hawera fault, through which methane gas is known to leak
• First blast is believed to have happened at 1530 (0230 GMT) on Friday, 19 November
• Two injured miners emerged from the tunnel entrance on Friday evening
• Second explosion on 24 November