At least 100,000 people in Hawaii were ordered to move from the shoreline to higher ground late on Saturday after a tsunami warning, but the first waves were less forceful than had been feared and no damage was initially reported.
The tsunami, triggered by a powerful earthquake off Canada's Pacific coast, began shortly after 10:30 p.m. Hawaii time, according to the Pacific Tsunami Warning Center, as motorists clogged roadways in a mass exodus from low-lying areas.
"The tsunami arrived about when we expected it should," Senior Geophysicist Gerard Fryer told reporters at a news conference, saying: "I was expecting it to be a little bigger."
The height of the first surge initially was put at 3 feet, but the warning center subsequently reported that early tsunami wave activity peaked at just 2.5 feet at the island of Maui.
There were no immediate reports of serious flooding or damage, but officials warned that additional waves were still possible and that wave heights of up to 6 feet could be reached in some places.
Following the initial surge, Honolulu Mayor Peter Carlisle said it was unclear if the worst had yet passed.
"All of these events are capricious, and you can't really tell which wave is going to be packing the most punch, and sometimes it's the second, third or even the very last one," he told CNN, adding that it might be several hours before officials could give the all-clear and cancel the evacuation.
Tsunami warning sirens in the islands were activated on short notice due to initial confusion among scientists about the quake's undersea epicenter and the extent of the tsunami threat posted by the temblor.
Honolulu Mayor Peter Carlisle announced that all police and emergency personnel were being pulled out from potential flood zones shortly before the first wave, leaving anyone defying evacuation orders to fend for themselves. He urged motorists who remained caught in harm's way due to gridlocked roads to abandon their vehicles and proceed on foot.
"If you are stuck in traffic, you might consider getting out of your car and consider walking to higher ground. You will have to assess your own situation, depending on where you are right now. Right now it is critical," he said
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 centered 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 was followed by numerous aftershocks as large as magnitude 4.6 and that a small tsunamihas been recorded by a deep-ocean pressure sensor.
On Oahu, Hawaii's most populous island, tsunami warning sirens could be heard blaring out across Honolulu, the state capital, prompting an immediate crush of traffic, with many motorists stopping at service stations to top up with gasoline. At movie theaters, 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 Honolulu's famed Waikiki Beach, residents of high-rise buildings were told to move to the third floor or higher for safety.
Stephany Sofos, a resident of Diamond Head near Waikiki, said most people had either evacuated or relocated to a higher floor.
"I moved my car up the hill, packed up my computer and have my animals all packed and with me," Sofos said, saying that she had not yet seen any obvious receding of the surf, a telltale sign that a tsunami wave is imminent.
"I'm pretty confident because we have a lot of reefs out there and that will prevent any major damage. Maybe it's a false confidence, but I'm not really worried," she said, adding, "It is nerve-wracking."
Tsunami Warning Center Geophysicist Gerard Fryer said the tsunami 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.
A tsunami advisory was also posted for coastal areas of northern California and Oregon, where a maximum sea level rise was estimated at 6 inches, the National Weather Service said. The agency said no significant flooding was expected.