Officials in Hawaii cancelled a tsunami advisory for the state's coastline, paving the way for beaches and harbors to reopen after widespread fears of waves generated from a powerful earthquake off the coast of Canada.

The Pacific Tsunami Warning Centre lifted its tsunami advisory Sunday morning just before 4am local time (3am today, NZ time), three hours after downgrading from a warning and less than six hours after the waves first hit the islands.

Centre officials said wave heights were diminishing, though swimmers and boaters should be careful of strong or unusual currents.

The biggest waves - about 1.5 metres high - appeared to hit Maui. A popular triathlon set for the island was expected to go on as planned, with county lifeguards giving the OK for a 1600m ocean swim.

There were no immediate reports of damage, though one person died in a fatal crash near a road that was closed because of the threat near Oahu's north shore.

Hawaii Governor Neil Abercrombie said the state was lucky to avoid more severe surges.

"We're very, very grateful that we can go home tonight counting our blessings," Abercrombie said.

Meanwhile, the National Weather Service cancelled tsunami advisories for Canada, Alaska, Washington, Oregon and California.

At first, officials said Hawaii wasn't in any danger of a tsunami after the 7.7-magnitude earthquake, which sparked tsunami warnings for southern Alaska and western Canada.

Later, officials issued a warning for Hawaii as well, saying there had been a change in sea readings. About the same time, a tsunami advisory was issued for a 724 kilometre stretch of US coast running from north of San Francisco to central Oregon.

A small tsunami created by the quake was barely noticeable in Craig, Alaska, where the first wave or surge was recorded.

The warning in Hawaii spurred residents to stock up on essentials at gas stations and grocery stores and sent tourists in beachside hotels to higher floors in their buildings. Bus service into Waikiki was cut off an hour before the first waves, and police in downtown Honolulu shut down a Halloween block party.

Abercrombie proclaimed an emergency, mobilising extra safety measures.

In Alaska, the wave or surge was recorded at 10cm, much smaller than forecast, said Jeremy Zidek, a spokesman for the Alaska Department of Homeland Security and Emergency Management. The first wave hit Craig about two hours after the earthquake.

A dispatcher with the Del Norte County Sheriff's said no damage was reported in Crescent City, a tiny fishing community in far Northern California, or in any other locations along the county's coast.

A tsunami warning means an area is likely to be hit by a wave, while an advisory means there may be strong currents, but that widespread inundation is not expected to occur.

- AP