(Recasts, adds detail)
HONOLULU, Oct 27 (Reuters) - Hawaii was bracing itself for a tsunami on Saturday night after an official warning was issued, prompting the evacuation of all low-lying areas in the island state, after a 7.7 magnitude earthquake struck off the coast of Canada's British Columbia.
The Pacific Tsunami Warning Center issued the alert, saying the first tsunami wave could strike the islands at 10:28 p.m. Hawaii Standard Time.
Vindell Hsu, a geophysicist at the Tsunami Warning Center said an estimated 100,000 to 150,000 people who live in Hawaii's coastal zones had been urged to move to higher ground until after 10:30 p.m.
Governor Neil Abercrombie issued an emergency proclamation for the state.
The tsunami center cautioned that wave height could not be predicted and that the first wave "may not be the largest".
It said: "All shores are at risk no matter which direction they face".
The warnings followed a powerful earthquake with a magnitude of 7.7 that hit Canada's Pacific coastal province of British Columbia late on Saturday.
The U.S. Geological Survey said the quake was centred 123 miles (198 km) south-southwest of Prince Rupert at a depth of 6.2 miles (10 km).
The Earthquakes Canada agency said the quake in the Haida Gwaii region was followed by numerous aftershocks as large as 4.6 and that a small tsunami has been recorded by a deep-ocean pressure sensor.
In Hawaii, tsunami warning sirens could be heard blaring out across Honolulu, the state capital on Oahu, the state's most populous island, prompting an immediate crush of traffic, with many motorists stopping first at service stations to top up with petrol.
At cinemas, films were halted in mid-screening as announcements were made urging patrons to return to their homes.
The last time Oahu had a tsunami warning was after the devastating Japanese earthquake of March 2011.
On Waikiki Beach, residents of high-rise buildings were told to move to the third floor or higher for safety.
Tsunami Warning Center Geophysicist Gerard Fryer said the tsunami danger had caught scientists by surprise.
"We thought that the earthquake was on land and when we learned that it was deeper undersea and we gathered more information, we had no choice but to issue a warning," he said
As residents scrambled to reach higher ground on Oahu, at least four major road accidents were reported by the state Emergency Medical Services. More accidents were also reported on the outer islands. (Reporting by Jorene Barut and Suzanne Roig in Honolulu; Writing by Steve Gorman and Tim Gaynor; Editing by Andrew Osborn)