A 15-month-old baby boy has become the fourth Australian fatality of the Samoa earthquake and tsunami which has devastated the Pacific nation, killing 149 people.

News of the baby boy's death came as 26 Australians arrived in Brisbane two days after surviving the 8.1 magnitude quake.

Six Australians who were unaccounted for were found safe and well on Thursday morning, but Foreign Minister Stephen Smith expressed concern that Australians who had not registered their travel plans could still be in the disaster zone.

So far, four Australians and a two-year-old permanent resident from New Zealand have been included in the official death toll, following the Samoan quake and subsequent tsunami that struck early on Tuesday morning.

The baby boy is yet to be named but the other Australians confirmed dead include 56-year-old Ballarat school teacher Vivien Hodgins, Tasmanian horse trainer Maree Blacker, who was in Samoa celebrating her 50th birthday, and a six-year-old girl.

The survivors were flown to Brisbane on Thursday afternoon aboard a government-chartered flight.

The 25 uninjured Australians, and one permanent resident, were offered counselling as they arrived aboard a Boeing 737 which had earlier delivered medical supplies and doctors to Samoa.

None of the passengers needed medical help, Emergency Management Queensland spokesman Tim Davey told reporters.

Mr Smith, however, was concerned that more Australians, who had not registered their travel plans with the Department of Foreign Affairs, could be in the disaster area.

"What we don't know is whether there were Australians in Samoa who were not known to us either because of registration through Smart Traveller or because of other sources," Mr Smith told reporters in Perth.

"We will need a few more days to make certain of that."

Mr Smith said none of the survivors had life-threatening injuries.

"... Those Australians who have been injured, I'm advised none of the injuries are life threatening but some of them are serious, very serious rib injuries and the like," he said.

A RAAF C-17 transport aircraft, which arrived in Samoa on Thursday with medical supplies and personnel, is due to land in Brisbane early Friday with another group of Australians.

Another charter plane was due to leave Brisbane on Thursday night and an RAAF Hercules, which was in New Zealand, has also taken supplies to the Pacific nation.

Mr Smith said Australia was coordinating its response closely with New Zealand, as part of a Pacific disaster agreement between Australia, New Zealand and France.

But seismologist and Australian Earthquake Engineering Society president Kevin McCue said Australia needed to help its Pacific neighbours revamp their outdated earthquake monitoring equipment.

"The Australian government does nothing, waiting to respond when these glaring deficiencies are highlighted in the next earthquake, tsunami or cyclone," Mr McCue said from Canberra.

The quake at Samoa and American Samoa was followed on Wednesday night by two major earthquakes just hours apart that stuck Indonesia's Sumatra island.

At least 529 people have been killed, Indonesia's social affairs ministry said on Thursday.