TAIPEI, Taiwan — A powerful quake struck off southwestern Taiwan today, triggering a potentially destructive tsunami that was headed toward the Philippines on the second anniversary of the deadly waves that killed thousands in South Asia.

The quake, with a preliminary magnitude of between 6.7 and 7.2, was felt throughout Taiwan. It collapsed two homes in the southern city of Pingtung, trapping six people, ETTV cable news reported. The quake also triggered fires and gas leaks, the station said.

No deaths were immediately reported.

Japan's Meteorological Bureau said a 3-foot-high tsunami was expected to hit Basco in the Philippines, about 125 miles southeast of the quake's epicenter.

"There is a possibility of a destructive local tsunami," the bureau said. "However at some coasts, particularly those near the epicenter, higher tsunami may arrive."

The Hawaii-based Pacific Tsunami Warning Center said there was no threat of a destructive Pacific-wide tsunami, based on historical earthquake and tsunami data, but that they would not know for about an hour what the threat might be to Taiwan or the Philippines.

Taiwan's Central Weather Bureau said the quake measured magnitude 6.7; the U.S. Geological Survey estimated it at 7.1; and the Japanese bureau put it at magnitude 7.2.

Temblors of magnitude 7 or higher are generally classified as major earthquakes, capable of widespread, heavy damage.

The Central Weather Bureau said a 6.4 magnitude aftershock struck a nearby area about nine minutes later.

The initial tremor was centered at sea about 13 miles southwest of Hengchun on the southern tip of Taiwan, the bureau said. Hengchun is about 260 miles south of Taipei.

A magnitude 9.1-magnitude earthquake off the coast of Indonesia on Dec. 26, 2004, caused a tsunami that killed at least 230,000 people in 11 countries. Those waves reached as high as 33 feet.

Unlike wind-driven surface waves, tsunamis are caused by seismic activity such as undersea earthquakes, landslides or volcanoes.

That means tsunamis are deep, reaching all the way to the seafloor, so that when they reach land they are forced upward into sometimes towering walls of water that can inundate coastal communities.