A powerful tsunami generated by an undersea earthquake killed more than two dozen people and wiped out several villages in the tropical islands of American Samoa and Samoa early on Tuesday, according to officials and local residents who were working to assess the damage. Christopher Moore of the National Oceanic and Atmospheric Administration looked at projected tsunami travel times at the Pacific Tsunami Warning Center in Ewa Beach, Hawaii. (Many tsunami warnings were later canceled.) earthquake struck around dawn, as many residents were preparing for work and getting their children ready for school. Officials said they expected heavy damage in the southern parts of Samoa and American Samoa, a United States territory with about 60,000 residents.Damaged telephone lines on both islands hampered efforts to count the casualties and assess the damage from earthquake, with a magnitude of 8.0. It struck below the ocean about 120 miles southwest of American Samoa and 125 miles south of Samoa and was centered only 11 miles below the seabed, according to the Filipo Ilaoa, the deputy director of the Honolulu office of Gov. Togiola Tulafono of American Samoa, said the number of people killed in American Samoa was “at least in the teens.” He said the toll would probably increase as emergency workers gained access to damaged areas.The Pacific Tsunami Warning Center at Ewa Beach, Hawaii, raised a regionwide alert that extended from American Samoa to New Zealand, though minimal damage was reported elsewhere. Tsunami awareness is relatively high in this earthquake-prone part of the world, particularly after the devastating earthquake and tsunami on Dec. 26, 2004, that killed 227,898 people around the Indian Ocean, according to the United States Geological Survey. Even so, Mr. Ilaoa said that the tsunami struck the coast of American Samoa in “a matter of minutes” after the quake, and that many residents would not have had much time to run for higher ground. “American Samoa is a small island and most of the residents are around the coast line,” he said. “There are very few villages inland, and so the problem comes when the wave hits unexpectedly. There was no warning or anything at all. By the time the alert was out of the Pacific Tsunami Warning Center, it had already hit.”On nearby Samoa, there were reports of at least a dozen casualties. Russell Hunter, the managing editor of the Samoa Observer newspaper in Vaitele, outside the capital, Apia, said his reporters had received word that at least 17 people on the island had been killed. Samoa’s police office did not respond to telephone calls and phone lines on much of the island were cut or jammed. “There is extensive damage in the southeast part of the island,” Mr. Hunter said. “It seems to be mostly in the rural villages.” He said that these villages were mostly clustered along the coast and that the houses were generally made of light materials, including wood. Many residents told local reporters of flattened houses and cars that were swept into neighboring towns by the churning waves. Graeme Ansell, a New Zealand tourist who was at Faofao Beach Fales on the southeast coast of Upolu Island, told Radio New Zealand that the village had been decimated. Mr. Ansell told the station he and others had clambered up a nearby hill to safety, and that one person he was with had sustained a broken leg.