Nine Australian military personnel were killed when their helicopter crashed during relief operations on the quake-hit Indonesian island of Nias.
Nias bore the brunt of Monday night's earthquake
Another two military personnel were seriously injured when the Sea King came down late on Saturday near the main town of Gunung Sitoli.
Australian Prime Minister John Howard said the incident was "heart-breaking" and would be investigated.
An estimated 1,300 people were killed in Monday night's earthquake.
Aid workers from around the world have arrived on the island to bring relief supplies and rescue survivors.
The helicopter was from an Australian navy medical ship, the HMAS
Kanimbla, which arrived at the island on Saturday, after providing tsunami relief for three months in Indonesia's Aceh province.
Those killed in the crash were five sailors from the Australian navy, three air force personnel and one army officer.
The pilot had not reported any problems before the crash.
"We're not sure (what went wrong). We know the helicopter
was flying at low height about the time the crash occurred," Gen Peter Cosgrove told reporters in the Australia capital, Canberra.
The BBC's Rachel Harvey, on the Indonesian island of Sumatra, says outside help is desperately needed on Nias, and helicopters are the only effective way of distributing aid and evacuating casualties from more remote areas of the island.
Poor weather has made flying difficult and rescue teams have still to reach remote parts of the island.
It has also affected conditions at sea. A boat chartered by a German aid agency has gone missing with six people on board.
Earlier on Saturday, the morale among rescue workers was boosted when a man was pulled alive from the rubble in Gunung Sitoli.
One international aid agency, Oxfam, said on Saturday that aid workers were on the move at last.
"People are moving out of town for the first time in a serious way today," Oxfam official Alex Renton told Reuters news agency by telephone from Gunung Sitoli.
"Outside town, things are still very unclear," he said, adding that he believed only about 10% of the 5,600 sq km (2,100 sq mile) island had been assessed by aid agencies.
The Indonesian government has said there is no food shortage but problems with distribution, and has promised to send more helicopters and ships from the mainland.
Gunung Sitoli has been without electricity, and the water purification system has been down.