Last night, the fatalities on Samoa and American Samoa had climbed to an estimated 106, including at least one New Zealander and two Australians.
Dozens of others were missing and many others were injured.
At least seven people were killed in Tonga.
Up to 1000 people were thought to have been displaced by the giant waves, which swept in about 20 minutes after the big quake.
Most of the deaths appeared to have occurred on the exposed southern coast of Upolu island in Samoa.
The popular resort area was left devastated.
As many as 20 villages were thought to have been destroyed.
Witnesses described the scene as one of complete annihilation, with villages and tourist resorts alike reduced to rubble by the force of the tsunami.
Cars and people were swept out to sea by the fast-churning water as survivors fled to higher ground, where they remained huddled hours after the quake struck about 6.48am on Tuesday local time (6.48am yesterday New Zealand time).
Samoan Prime Minister Tuilaepa Sailele Malielegaoi was "shocked beyond belief" by the destruction.
Looking shaken and distressed, he described it as an "unimaginable" tragedy.
"So much has gone.
''So many people are gone," the Prime Minister said on board a flight from Auckland to the Samoan capital of Apia late yesterday.
"I'm so shocked, so saddened by all the loss."
It is understood a large number of the dead are children or elderly, as they could not escape the tsunami.
New Zealand-educated resort owner Anna Tui Annandale - one of Samoa's richest women - drowned trying to rescue children, Samoa's deputy prime minister, Misa Telefoni, said.
Throughout the island nation, signs of the disaster were everywhere, with a large boat which had been washed ashore lying on the edge of a highway and floodwaters swallowing up cars and homes.
The quake, with a magnitude of 8.3 on the Richter scale, struck about 200km from Samoa, which has a population of about 180,000, and about 190km from neighbouring American Samoa, a United States territory of about 65,000 people.
Four tsunami waves 4m to 6m high roared ashore 20 minutes later, reaching up to 1.6km inland, Mike Reynolds, superintendent of the National Park of American Samoa, was quoted as saying.
The New Zealand Government last night reported the tsunami had left one New Zealander dead and nine injured.
Acting Prime Minister Bill English said about 150 New Zealanders had reported to the High Commission in Apia, 70 of them from the worst-hit resort areas.
"We have no further information about New Zealand fatalities and there won't be until Samoan authorities have identified the growing number of bodies that are coming in."
Mr English confirmed an air force Orion had reached Samoa to help search for people washed out to sea by the tsunami.
A Hercules transport aircraft had been due to leave about midnight with medical supplies and army medical personnel, as well as tents, food and temporary morgues requested by Samoa.
Mr English said some of the people turning up at the High Commission had lost everything.
"They have no passports, no clothes - they're being looked after in the best way possible."
The nine injured New Zealanders were in two hospitals in Apia, but he had no other details.
Australia's Department of Foreign Affairs and Trade said Australian woman Maree Blackler, of Tasmania, was among the dead in Samoa, three other Australians were in hospital and six others remained unaccounted for after the tsunami.
At least 22 people were killed on American Samoa, with reports of a further 50 injured.
United States President Barack Obama declared the aftermath a "major disaster".
Late in the afternoon, a further tsunami warning was issued for Samoa, resulting in low-lying parts of Apia being evacuated, although the tsunami did not eventuate.
Small tsunami waves caused by the quake even reached Japan yesterday, Japan's Meteorological Agency officials said.
• The Ministry of Foreign Affairs asked New Zealanders concerned about relatives in Samoa to call (04) 439-8000.
• A strong earthquake of magnitude 7.9 struck off the city of Padang on the coast of Indonesia's Sumatra island last night, damaging houses, bringing down bridges and starting fires, a witness said.
A regional tsunami warning was issued, the Pacific Tsunami Warning Centre said.
It was unclear if there were any casualties. - AP/AAP/NZPA
