updated 11/29/2004 2:53:17 AM ET 2004-11-29T07:53:17

A powerful earthquake with a preliminary magnitude of 7.1 struck Japan's northern island of Hokkaido early Monday, injuring at least 14 people, swaying buildings and triggering a small tsunami wave that reached the shore.

Damage from the 3:32 a.m. quake appeared to be limited to broken glass, cracks and at least one caved-in roof.

Japan's Meteorological Agency quickly issued a tsunami warning for the eastern shores of Hokkaido's Pacific coastal area. Tsunami are potentially dangerous waves triggered by seismic activity.

But agency official Masahiro Yamamoto later told a televised news conference that the warning had been lifted, saying it had detected a 4-inch tsunami and expected only small changes in the ocean's surface.

The quake was centered off Hokkaido's east coast, about 550 miles northeast of Tokyo, 30 miles below the sea surface. The rocking was felt throughout northern Japan, including Hokkaido's largest city, Sapporo, and Kushiro, on the island's eastern shore.

A 4.6-magnitude aftershock followed the initial tremor about a half hour later.

"We expect the aftershocks to continue," said Yamamoto, adding that a quake of this magnitude only happens about once every decade.

National broadcaster NHK showed footage of desks rumbling in their offices and convenience store goods thrown from shelves by the force of the quake.

Most of the injuries were in the cities of Kushiro, Nemuro and Bekkaicho. An 81-year-old woman living in Nemuro was thrown to the floor and treated for a broken arm, and several others, mostly elderly, had suffered minor injuries such cuts from falling objects or broken glass, Hokkaido prefectural police spokesman Tsuneo Sasaki said.

In Kushiro, a 57-year-old woman suffered a foot injury after stepping on broken glass, police said.

More than 1,500 homes in Hokkaido briefly lost power, said Hokkaido Electric Power Co. spokesman Junichiro Kato. Natural gas services to many homes were also cut but quickly restored.

Cracks were discovered in Nemuro city's docks and at least two schools had broken windows and cracked water pipes, city spokesman Atsushi Maeda said. A school corridor roof collapsed partially, but nobody was injured from it, police said.

Railway services on several lines in Hokkaido were suspended for a short time, according to NHK.

A magnitude 7 earthquake can cause widespread and serious damage if centered in a heavily populated area. Monday's quake was centered deep enough below the ocean floor that much of its power was absorbed by the time its tremors reached land.

Last month, a 6.8-magnitude earthquake and several large aftershocks in northern Niigata prefecture killed 40 people and damaged over 16,000 homes. That quake was the deadliest to hit Japan since 1995, when a 7.2-magnitude quake killed 6,000 people in the western city of Kobe.

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