Whole villages on the Samoan coast were wiped out by the wave and health workers have reported more than 100 dead with many more missing or unaccounted for.
The tsunami followed and 8.3 magnitude earthquake.
One of the Australians who died was Tasmanian woman Maree Blacker, of Longford.
She had been celebrating her 50th birthday.
A six-year-old girl, a 56-year-old woman from Victoria and a two-and-a-half-year-old New Zealander with Australian residency have also been killed.
One other Australian is still unaccounted for.
Horror stories are emerging of the scene along the Samoan coastline.
One nzherald.co.nz reader received a short-wave radio message from relatives in the low-lying village of Salesatele, saying that "37 bodies have been found".
New Zealander Graeme Ansell said the beach village of Sau Sau Beach Fale was leveled.
"It was very quick. The whole village has been wiped out," Ansell told New Zealand's National Radio from a hill near Samoa's capital, Apia.
"There's not a building standing. We've all clambered up hills, and one of our party has a broken leg. There will be people in a great lot of need 'round here."
An Associated Press reporter saw the bodies of about 20 victims in a hospital on the main island of Upolu and said the surrounding tourist coast was devastated.
Update your news preferences and get the latest news delivered to your inbox.