PALMER, ALASKA, NOV. 30 -- A major offshore earthquake rocked south-central Alaska today, prompting thousands of people to flee low-lying coastal areas for the second time in two weeks.

No major damage or injuries were reported in the quake, which measured at least 7.4 on the Richter scale. It shook the ground for a full minute and was felt more than 300 miles from the epicenter, in Anchorage and the Yukon Territory.

A warning of a tsunami, or giant sea wave, was issued for Gulf of Alaska communities and British Columbia, and a tsunami watch was issued for Washington, Oregon, California and Hawaii. But they were canceled after 90 minutes when a 3.3-foot wave was recorded at Yakutat, the community closest to the epicenter.

The quake at 10:23 a.m. Alaskan standard time was centered 100 miles southwest of Yakutat in the Gulf of Alaska, the center said. A quake measuring 6.9 on the scale shook the same area Nov. 16.

While the center reported the preliminary magnitude at 7.4, University of California seismographs measured it at 7.7 on the Richter scale.

Emergency sirens and police loudspeakers roused coastal Alaska residents from their homes and businesses and started them toward high ground. Residents of some Canadian communities were warned not to take out boats and airplanes because of strong winds and high waves.

In Yakutat, lights went out, and about 300 persons jammed a community high school. The greatest damage appeared to be broken water pipes and the power outage, which lasted about an hour, a school secretary said.

"This one was a low rumbler," City Manager Jim Filip said. "Most people in Alaska are used to earthquakes. But in my experience, this was a good one."

The emergency siren sounded in the southeast Alaska fishing community of Sitka shortly after the tsunami warning, and the community's streets were clogged with traffic as residents headed for high ground, said Sandy Poulson, co-publisher of the Sitka Sentinel.

More than 1,000 people evacuated low-lying areas and several villages around Kodiak Island, police Sgt. Nancy Perry said.

In the quake Nov. 16, residents fled to Pillar Mountain. "This time, several people going to Pillar found it so icy they had to head back," Perry said.

The quake occurred in the transition zone between the Pacific and North American plates of the Earth's crust, west of the Yakutat block, authorities said.

The destructive 1964 Alaska earthquake measured 8.5 on the Richter scale.