A tsunami warning prompted by a powerful earthquake off the Canadian coast sent at least 100,000 people fleeing from shore to higher ground in Hawaii late on Saturday, but an evacuation order was canceled after a series of weaker-than-expected waves rolled through the islands.
The warning was downgraded to an advisory – a lower-level alert – shortly after 1 a.m. Sunday (1100 GMT), though state civil defense authorities said beaches and harbors would remain closed for the time being, and residents were urged to stay away from the water.
There were no immediate reports of injuries, serious flooding or damage, but officials warned that abrupt changes in sea level and strong currents could still pose a hazard to swimmers and boaters.
"The threat may continue for several hours," the Pacific Tsunami Warning Center said in its alert.
While scientists had warned early on that waves as tall 6 feet (1.8 metres) could occur in places, tsunami wave activity was reported to have peaked at just 2.5 feet (0.8 metres) at the island of Maui shortly after 10:30 p.m.
"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."
Tsunami warning sirens began blaring across the islands at about 8 p.m. as state officials ordered a coastal evacuation, prompting a mass exodus that clogged roadways as motorists fled low-lying areas.
As the forecast arrival time of the tsunami neared, Honolulu Mayor Peter Carlisle announced that all police and emergency personnel were being pulled out from potential flood zones, leaving anyone defying evacuation orders to fend for themselves. He also 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 the evacuation affected an estimated 100,000 to 150,000 people who live in Hawaii's coastal zones.
Shelly Kunishige, a spokeswoman for Hawaii State Civil Defense, said evacuation orders were lifted once the tsunami warning was downgraded. But a thorough assessment of flooding or damage could not be made until after daybreak, she said.
The Earthquakes Canada agency said the temblor was followed by numerous aftershocks as large as magnitude 4.6 and that a small tsunami had 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.
"I moved my car up the hill, packed up my computer and have my animals all packed and with me," said Staphany Sofos, a resident of the Diamond Head community near Waikiki as she waited word for an all-clear that came several hours later.
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 reported on the outer islands. But Kunishige said no major injuries were reported.
A tsunami advisory was also posted for coastal areas of northern California and Oregon, where a maximum rise in the sea level was estimated at 6 inches (15 cm), the National Weather Service said. The agency said no significant flooding was expected.
* Reporting by Jorene Barut and Suzanne Roig in Honolulu; Writing by Steve Gorman and Tim Gaynor; Editing by Andrew Osborn and Eric Beech.