All 29 miners trapped in a coal mine in New Zealand are believed to be dead after a second explosion, police say.

新西兰警方称，所有被困于一座煤矿的29名矿工在经历第二次爆炸之后无人幸免。

Superintendent¹（监督人，负责人） Gary Knowles said the ignition（点火，燃烧） of gases in Pike River Coal mine meant a rescue was very unlikely.

"It is our belief that no-one has survived and everyone will have perished," he told reporters.

There had been no contact with the men - 24 New Zealanders, two Australians, two Britons and a South African - since the first explosion on Friday.

Supt Knowles said the second blast occurred just before 1500 local time on Wednesday. "It was extremely severe," he added. "I've had to break the news to the families and they're extremely distraught（发狂的） ."

The chief executive of the South Island mine, Peter Whittal, said his company would make every effort to retrieve²（恢复，救出） the bodies of the men.

"We want our boys back and we want to get them out," he told reporters.

Family members wept, shouted and fell to the floor after hearing the news, Grey District mayor Tony Kokshoorn said.

"It's unbelievable. This is the west coast's darkest hour," Mr Kokshoorn said. "It doesn't get worse than this."

It was not immediately clear what triggered the second blast.

Explosive and poisonous gases had been present in the mine since the initial explosion and had prevented rescuers from entering the mine to search for the missing men, who included a 17-year-old on his first shift.

Two robots had been sent into tunnels（隧道） of the mine and a third was on its way in the hope of gaining a clearer pictures of the conditions underground.

The first robot hat found the helmet（钢盔，头盔） of Russell Smith, one of the two miners to escape the blast on Friday.

Officials had become increasingly pessimistic（悲观的） about the chances of pulling the men alive from a network of tunnels some 1.5miles (2km) deep in the side of a mountain.