The wall of water triggered by the 8.0-magnitude quake -- which witnesses said was up to five metres (16.5 feet) high -- swamped towns, flattened homes, and sparked panic among residents of the impoverished South Pacific state.

Communications to the quake-hit area were patchy, making it difficult to assess the number of dead and injured and the damage, Prime Minister Manasseh Sogavare told CNN.

The Pacific Tsunami Warning Centre issued a regionwide warning immediately after the quake, stretching as far away as Japan, but later cancelled it.

At least 15 people were killed in and around Gizo, the main town in Western Province and a popular tourist and diving spot 40km from the quake's epicentre, the provincial leader said.

"Reports have come in that more than 15 people died, just around Gizo, but with the other islands I cannot tell you," premier Alex Lokopio told Radio New Zealand.

The central government reported 12 deaths and the police at least four, but Sogavare warned the death toll would likely rise once rescue teams reached the area.

"Most of the islands are low-lying, and the extent of the damage is yet to be known," the prime minister said, adding that a team from his office, the Red Cross and the police were headed to the area.

"It's a very trying time for us."

In the capital Honiara, the head of the Solomons National Disaster Council, Fred Fakari, told journalists: "Some villages are completely wiped out."

The government's communications unit reported six bodies found floating in seas near Gizo town, hours after the shallow quake struck at 7:40 am (2040 GMT Sunday).

The US Geological Survey reported a series of aftershocks measuring up to a magnitude of 6.7.

Across the Pacific, governments from Australia to New Caledonia and the Northern Marianas evacuated schools and ordered coastal residents to move to higher ground, but no damage was immediately reported.

Lokopio, the premier of Western Province, said there was a desperate need for emergency supplies in the Gizo area, where residents remained on a hill behind the town amid strong aftershocks.