Water rushed up on roadways and into hotel lobbies on the Big Island and low-lying areas in Maui were flooded as 7-foot waves crashed ashore. Smaller waves hit the U.S. western coast and beaches were closed as fishermen fired up their boats and left harbors to ride out the swell.
Photos: Scenes from the earthquake
Scientists warned that the first tsunami waves are not always the strongest, and officials said people in Hawaii and along the West Coast should watch for strong currents and heed calls for evacuations. The tsunami warning was downgraded to an advisory in Hawaii, but officials said people should still stay away from beaches.
"I'm waiting to see if I'll be working and if I can get to work," said Sabrina Skiles, who spent the night at her husband's office in downtown Kahului in Maui. Their home, across the street from the beach, was in a mandatory evacuation zone. "They're saying the worst is over right now but we keep hearing reports saying 'don't go anywhere. You don't want to go too soon.'"
The tsunami, spawned by an 8.9-magnitude earthquake in Japan, slammed the eastern coast of Japan, sweeping away boats, cars, homes and people as widespread fires burned out of control. It raced across the Pacific at 500 mph - as fast as a jetliner - before hitting Hawaii and the West Coast.
Sirens sounded for hours before dawn up and down the West Coast and in Hawaii, and roadways and beaches were mostly empty as the tsunami struck.
Videos of the earthquake
President Barack Obama said the Federal Emergency Management Agency is ready to come to the aid of any U.S. states or territories who need help. Coast Guard cutter and aircraft crews were positioning themselves to be ready to conduct response and survey missions as soon as conditions allow.
It is the second time in a little over a year that Hawaii and the U.S. West coast faced the threat of a massive tsunami. A magnitude-8.8 earthquake in Chile spawned warnings on Feb. 27, 2010, but the waves were much smaller than predicted and did little damage.
Scientists then acknowledged they overstated the threat but defended their actions, saying they took the proper steps and learned the lessons of the 2004 Indonesian tsunami that killed thousands of people who didn't get enough warning.
This time around, the warning went out within 10 minutes of the earthquake in Japan, said Gerard Fryer, a geophysicist for the Pacific Tsunami Warning Center in Honolulu.
"We called this right. This evacuation was necessary," Fryer said. "There's absolutely no question, this was the right thing to do," he said.
The warnings issued by the tsunami center covered an area stretching the entire western coast of the United States and Canada from the Mexican border to Chignik Bay in Alaska.
Many islands in the Pacific evacuated, but officials later told residents to go home because the waves weren't as bad as expected.
In Guam, the waves broke two U.S. Navy submarines from their moorings, but tug boats corralled the subs and brought them back to their pier. No damage was reported to Navy ships in Hawaii.
In the Canadian pacific coast province of British Columbia, authorities evacuated marinas, beaches and other areas.
Officials in two coastal Washington counties used an automated phone alert system, phoning residents on the coast and in low-lying areas and asking them to move to higher ground.
"We certainly don't want to cry wolf," said Sheriff Scott Johnson of Washington's Pacific County. "We just have to hope we're doing the right thing based on our information. We don't want to be wrong and have people hurt or killed.