HONOLULU (AFP) - Tsunami waves raced across the vast Pacific Ocean Friday triggered by a huge quake off Japan, washing ashore in Hawaii and threatening the US West Coast, as officials urged people to seek shelter.

   Sirens blared and Hawaiian authorities rapidly evacuated low-lying areas as the waves rolled across thousands of miles from the Japanese coast to hit Hawaii before dawn around 3:24 am (1324 GMT).

   Many residents had already taken refuge in shelters, after the Pacific Tsunami Warning Center issued an ocean-wide alert for the giant waves along the West Coast, down through Central and South America as far as Antarctica.

   Canada also issued an alert for the north coast of British Colombia, warning it may "produce strong currents dangerous to those in or near the water."

   The tsunami warning came after an 8.9-magnitude quake hit Japan, the largest ever recorded in the Asian nation's history, triggering walls of water which swamped the Japanese coastline and left more than 330 people dead.

   The largest wave to crash ashore in Hawaii -- some 4,000 miles (6,500

kilometers) from the epicenter of the quake -- was measured as a six-foot

(1.8-meter) surge that hit Kahului on the island of Maui, officials said.

   The US states of California and Oregon were also on alert, with the first surge due to wash over the northern California coast from 8:30 am (1630 GMT).

   Authorities there urged residents to leave beaches and coastal areas and warned that sea currents could become hazardous.

   "Current intelligence indicates a 3-foot (one-meter) surge may impact the coastline of Los Angeles County," said county fire captain Sam Padilla, adding heightened waves could continue for 10-12 hours.

   In Hawaii, geophysicist Gerard Fryer with the Pacific center said it was a "significant tsunami."

   The first huge six-foot wave was followed about 15 minutes later by a second wave of some five feet, according to deep sea monitors.

   Fryer told a press conference the first wave grew over 10 minutes to that height and then dropped back. There were no reports of significant damage, but waves had apparently been washing up about 100 feet (30 meters) inland on the Big Island.

   US President Barack Obama said he was monitoring the tsunami threat to his home state of Hawaii and the US West Coast, and he phoned Japanese Prime Minister Naoto Kan to offer condolences and US help.

   "I have instructed FEMA (the Federal Emergency Management Agency) to be ready to assist Hawaii and the rest of the US states and territories that could be affected," he said.

   The Pentagon said the US military was ready to provide emergency assistance to the victims in Japan, and especially to send ships with humanitarian aid to help.

   US military forces in the Pacific "are assessing the situation and positioning forces so we are ready to respond and provide disaster relief if requested," said Pentagon spokesman David Lapan.

   Californian search and rescue teams were also on standby to help out if needed -- only a day after returning from the recent New Zealand quake, the Los Angeles County Fire Department said.

   Meanwhile, the USS Dubuque that was docked south of Los Angeles was ordered out into open water as a precautionary measure.

   But the US Pacific Fleet command said it would not evacuate any personnel or sailing ships out of Pearl Harbor, on the southeastern side of Oahu Island, Hawaii.

   Hawaiians had scrambled late Thursday to stock up on fuel, and arguments broke out as lines formed in front of gas stations in the hours before the wave hit, the Star Advertiser newspaper reported.

   Local resident Jake Chang was filling up his truck and a plastic gas container to power his generator. "I was watching TV," he told the newspaper.

"I saw the footage of Japan. It was unreal."

   A separate warning issued by an Alaska monitoring station extended to Hawaii, the northern and central California coast, the Oregon coast, and parts of Alaska. It urged residents to move inland and to higher ground.

   "With an earthquake of this size, we could definitely see some water on the West Coast," said Cindi Preller, a watcher at the center.