A tsunami warning was in effect across the south and southeast Alaska and the west coast of Canada and the remainder of the US West Coast was under a watch following a powerful earthquake that struck off the coast of northernmost US state. The 7.9 magnitude quake struck at 0931 GMT in the Gulf of Alaska, 280 kilometers (175 miles) southeast of the town of Kodiak, the US Geological Survey said, revising a preliminary estimate of 8.2 magnitude. The epicenter was 10 kilometers under the seabed. Less-ominous tsunami watches were issued for the US west coast -- the entire coasts of California and Oregon and part of Washington state -- and Hawaii out in the Pacific. Tsunami waves could hit the coasts of Oregon and Washington as early as around 1310 GMT, the Portland office of the National Weather Service said. Heather Rand, who was 360 miles away in Anchorage, told CNN it felt like the longest earthquake she had ever experienced. "It was a very long, slow build up. Creepy, more than anything. Definitely the longest, and I was born here," Rand said, adding the only damage was cracks in the wall. So far no quake damage or large waves have been reported in Kodiak, which is on an island off the coast, police spokesman Tim Putney told AFP. "We are half an hour beyond the time we were told the first wave might hit. Nothing has happened," he said around 1115 GMT. "We have people with their eyes on the sea, from a safe distance," Putney added. Still, authorities urged coast dwellers to seek safety. "If you are located in this coastal area, move inland to higher ground," the Anchorage Office of Emergency Management said. "Tsunami warnings mean that a tsunami with significant inundation is possible or is already occurring. Tsunamis are a series of waves dangerous many hours after initial arrival time. The first wave may not be the largest." However, officials were telling people to hold fast at evacuation centers until further notice. Putney said the town has several shelters above the 100-foot mark, and they were still encouraging people below that level to evacuate. The earthquake woke Putney up out of a dead sleep, and he estimates it shook for at least 30 seconds. Larry LeDoux, superintendent of the Kodiak Island Borough School District, said schools were open as shelters and estimated there were about 500 people at the high school. He described the atmosphere inside as calm, with people waiting for any updates. He said sirens go off in the community every week, as a test to make sure they are working. He said the sirens were sounded for the early Tuesday tsunami warning.