At least 19 people have died, more are reported to have been swept out to sea, and whole villages have been wiped out after a powerful 8.3-magnitude earthquake sent tsunami waves smashing into the coast of Samoa this morning.

The Pacific Tsunami Warning Centre has now downgraded its Pacific-wide warning. New Zealand had been bracing for the tsunami to hit its east coast but there have been no reports of damage from the impact so far.

The tsunami was generated by a magnitude-8.3 earthquake which struck 190 kilometres southwest of American Samoa.

At least 14 people have been reported dead in American Samoa and at least five in Samoa. There were reports that three children died in Samoa as the tsunami flattened houses and swept away cars.

There are also fears for the fate of the island communities between Samoa and New Zealand, with three-metre waves reported from the area.

A reporter for Radio Polynesia told Radio New Zealand that villages were "wiped out" by the tsunami and people had been reported missing.

The Samoan capital Apia has been evacuated and thousands of people have been moved to higher ground. Neighbouring American Samoa has also been severely damaged by the 'quake and tsunami and it is expected casualties will be high.

A spokesman for New Zealand's Foreign Affairs Minister Murray McCully says the minister's office has received reports of five people dead in Samoa and "many more washed out to sea".

The general manager of Southseas Broadcasting, Joey Cummings, said cars were swept out to sea and the water reached the second floor of the Pago Plaza building in the American Samoa capital Pago Pago.

Vincent Ilui from the village of Leone in American Samoa says the tsunami struck so quickly some people were drenched when they arrived on higher ground.

"Currently it's been announced on the radio, from the emergency operating centre ... that there's been 14 reported deaths so far and six of them are here in my village," he said.

Olga Keil, a journalist working in Samoa, described the damage.

"We've got reports from the south-eastern side of the main island, where houses have been completely flattened, vehicles have been swept out to sea, boulders that have fallen of the mountain along the coastal areas," she said.

"But mainly a lot of houses in the villages on the coastal areas have been flattened by the waves."

Parliamentary Secretary for International Development Assistance Bob McMullan says a number of Australians have been injured but they have all received appropriate treatment and are stable.

"All of them have been able to contact their own families directly and none of them have said to the High Commission they need any special or extra assistance," he said.

"The reports from Australians suggest it was a very frightening event for people, both the extent of the earthquake and the impact of the tsunami, and we are now having to make very rapid contact with everybody."

Australian Nick Rees told ABC News Breakfast that his parents had called him to tell him the tsunami had hit the southern side of the main Samoan island, completely destroying their hotel.

"They've lost everything they have ... [but] they're alive and they're OK, my dad has broken some ribs," he said, adding that some people were missing from the hotel.

Mr Rees said he thought the guests had very little warning.

"There were people from their hotel missing... I'm assuming if dad's injured and there are people missing it was pretty quick," he said.

The Pacific Tsunami Warning Centre said waves 1.57 metres tall hit American Samoa, while 0.7 metre waves were recorded in Samoa.

New Zealanders have been told to expect waves making first landfall on the country's east coast, including East Cape and the city of Gisborne, soon. NZ's minister of civil defence has warned people to get off the country's beaches.

A brief statement issued by the Joint Australian Tsunami Warning Centre, operated by the Bureau of Meteorology and Geoscience Australia, said no Australian territory would be hit by the tsunami.

But senior meteorologist Tony Leggett says the New South Wales and Southern Queensland coastline could experience some unusual currents later this morning.

DFAT says Australians who are concerned about friends or relatives in the region can call a special hotline on 1300 555 135.

Russell Hunter, a journalist with the Samoa Observer, says the quake lasted a minute-and-a-half.

"There doesn't seem to be any damage around the capital. We are told there have been deaths on other side of the island as a result of the following tsunami - so far we are told three children in a small village on the other side of the island," he said.

Australian Miyako Armitage was working out in the gym of an Apia Hotel in Samoa when the earthquake hit.

"I thought that the men were rattling the weights a little bit too loudly, but it turned out to be quite a big earthquake," she said.

"So we ran out, as we stood around in the middle of the road we saw the building swaying quite a lot. That was quite scary."

The USA's Pacific Tsunami Warning Centre had earlier issued a tsunami warning for a large swathe of the South Pacific including Fiji, New Zealand and Tonga after the US Geological Survey (USGS) reported a 7.9 magnitude quake.

The centre later said an 8.3 magnitude quake had been recorded at a depth of 33 kilometres. It was not immediately clear if this was the same quake and the USGS's website did not provide exact details of its location.

In its preliminary earthquake report, the US Geological Survey put the epicentre 204 kilometres south-south-west of Samoa's capital Apia and at a depth of 85 kilometres.

The USGS said the region was struck by a 5.6 magnitude quake about 20 minutes after the first.