Investigators admitted Monday they were "a long, long way" from knowing why a sightseeing helicopter crashed into a New Zealand glacier, killing all seven people on board.

As bad weather halted efforts to recover more bodies from the chopper's wreckage at Fox Glacier, on the west coast of the South Island, it was revealed no mayday was sent from the helicopter before Saturday's crash.

Four British and two Australian tourists, as well as their New Zealand pilot, died when the helicopter plunged into the heavily-crevassed glacier during bad weather.

"We are a long, long way from identifying the circumstances and causes of this accident," Transport Accident Investigation Commission (TAIC) investigator Peter Northcote said.

Northcote said a full probe into the accident could take 18 months, with the immediate hunt for clues on hold due to poor weather at the crash site.
Specialist alpine rescuers managed to recover three bodies on Sunday but inspector John Canning said conditions were now not expected to clear until Wednesday.

"We've done the easy bits with the recovery so far from helicopters, but now we've got to put boots on the ice," he told reporters.

"To do that we're going to have to build a staging point and put equipment in place so that we can get our workers across there safely."

Alpine rescue team leader Marius Bron said ice on the glacier was loosely packed and constantly moving, with crevasses up to 20 metres (66 feet) deep.

"If you imagine a giant bowl of popcorn, the ice is all stacked up and unstable, there's lots of gaps in there, that's what we're dealing with," he said.

The dead were identified as Britons Andrew Virco, 50, and Katharine Walker, 51, of Cambridge; Nigel Edwin Charlton, 66, and Cynthia Charlton of Hampshire; along with Australians Sovannmony Leang, 27, and Josephine Gibson, 29, from Sydney.

Police were only alerted when the helicopter's emergency locator beacon was activated late Saturday morning.

Debris was later found scattered over several hundred metres with the main part of the helicopter wedged between house-sized blocks of ice.

The 13-kilometre-long (eight-mile) Fox Glacier is listed as one of the world's most accessible glaciers and attracts thousands of tourists each year.

There was another aviation crash in the area in September 2010, when nine people died after a skydiving plane plunged to the ground then burst into flames shortly after takeoff.