A mild tsunami hit Hawaii late Saturday after a powerful earthquake off the west coast of Canada, forcing a state-wide evacuation but apparently failing to cause major damage.
The center warned, however, that sea level changes and strong currents could still occur and present a hazard for swimmers and boaters.
"The threat may continue for several hours," the center cautioned.
Highways and roads in coastal areas were re-opened, allowing thousands of residents and hundreds of tourists to return to their homes and hotel rooms.
But the tsunami, set off by a powerful 7.7 magnitude earthquake that struck off the west coast of Canada, succeeded in disrupting the weekend activities of many tourists and residents.
Countless Halloween parties were interrupted, restaurants, bars and movie theaters emptied, and highways quickly filled with cars heading away from beach areas.
Tourists from Waikiki to Turtle Bay in Honolulu were evacuated to higher floors in their hotels, and major tourist centers looked abandoned for several hours.
Governor Neil Abercrombie declared a state of emergency when the first alert was sounded and kept it in force.
"We are taking a wait-and-see approach -- we want everyone to be safe," said the governor's spokesperson, Donalyn Dela Cruz.
Initially, the Pacific Tsunami Warning Center said there was no "destructive widespread tsunami threat" after the 7.7 magnitude quake shook the Queen Charlotte Islands off the west coast of Canada.
But later it issued a warning, saying a tsunami had been generated by the earthquake and that it was headed toward Hawaii.
Sirens blared across the archipelago as local officials took to the airwaves, urging residents to head for higher ground -- or higher floors if they were in multi-story buildings.
-- 'A 7.7 is a big, hefty earthquake' --
The epicenter of the Canadian quake, which occurred at 8:04 pm Saturday (0304 GMT Sunday) was located 139 kilometers (86 miles) south of the town of Masset, the US Geological Survey said.
Numerous aftershocks, some as strong as magnitude 4.6, followed the initial quake, Canadian officials reported.
Emergency officials in British Columbia urged residents in low-lying coastal areas to be alert to instructions from local officials and be prepared to move to higher ground.
"The tsunami alarm went off and everybody went to the evacuation site," Danny Escott, owner of the Escott Sportfishing lodge near Masset, told AFP by telephone.
But officials in Canada sought to calm the population.
"We would not be expecting any widespread damage or inundation," Kelli Kryzanowski of Emergency Management British Columbia told reporters during a teleconference.
Natural Resources Canada said in a statement that the quake was felt across much of north-central British Columbia, including Haida Gwaii as the Queen Charlotte Islands are also called, Prince Rupert, Quesnel, and Houston.
But the ministry also played down the effects on Canada, saying: "There have been no reports of damage at this time."
However, Gerard Fryer, a senior Geophysicist with the Pacific Tsunami Warning Center, said quakes exceeding magnitude 7.0 should not be taken lightly.
"A 7.7 is a big, hefty earthquake. It's not something you can ignore," he told CNN International.
He said it had struck partly under an island, but mostly under shallow water.
"I think we have to be thankful it happened where it did," Fryer said. "If that were a heavily populated area, it would have caused significant damage."
The earthquake reading was based on the open-ended Moment Magnitude scale used by US seismologists, which measures the area of the fault that ruptured and the total energy released.
The Queen Charlotte Islands, which are also known by their official indigenous name of Haida Gwaii, comprise about 150 islands located north of Canada's Vancouver Island. Their total population is about 5,000. The Haida people make up about 45 percent of the total population.