Sirens reportedly blared out across the Samoan capital, Apia, again late on Tuesday but the warning was thought to be a false alarm.
Dr Lemalu Fiu, at a hospital in Apia, said the number of casualties was expected to rise as people arrived from coastal areas bringing reports.
Mr Telefoni said there were fears the major tourism areas on the west side of Upolu island - the eastern of the two main Samoan islands - had been badly hit.
"We've had a pretty grim picture painted of all that coast," he said.
Australian Prime Minister Kevin Rudd confirmed the death of two Australians - a six-year-old girl and a 50-year-old woman.
Samoan officials say it could take a week before the full extent of the damage is known.
A government official in Tonga said at least six people had been killed there and four more were missing.
High waves damaged property and swept cars out to sea
But New Zealand's acting Prime Minister Bill English said Tongan officials had told him a "considerable number of people" had been swept out to sea.
Mr English added: "Over the next 12 hours the picture could look worse rather than better."
The Pacific Tsunami Warning Centre (PTWC) said the quake struck at a depth of 33km (20 miles), some 190km (120 miles) from Apia.
Radio New Zealand quoted Samoan residents as saying that villages were inundated and homes and cars swept away.
Graeme Ansell, a New Zealander near Apia, told the radio station the beach village of Sau Sau Beach Fale had been "wiped out".
"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 around here," he said.
Witnesses have reported scenes of destruction.
"It's horrible... The village is gone and my once beautiful beachfront villa has now been submerged in water," Josh Nayangu told the BBC after fleeing the area on a small fishing boat with his wife and son.
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