The quake jolted Japan's main northern island of Hokkaido at 3:32 amGMT Sunday), temporarily knocking out power to nearly 1,600 homes and prompting a one-hour alert for tsunami tidal waves, officials said.

"As I reached for the entrance door, lots of things just kept falling. I went outside with no shoes on and then realized my feet hurt. It was a very powerful quake," a woman in her 70s told public broadcaster NHK.

Hokkaido was shaken, after the initial quake, by six aftershocks measuring above 4.0 on the Richter scale, the Meteorological Agency official said.

A police spokesman in Hokkaido said at least 17 people were injured, including an 80-year-old woman who broke her arm after falling in her house and a 13-year-old boy whose leg was hurt by broken glass.

"Apart from the old lady, everyone had minor injuries and it was a relief that we had very few casualties," said police spokesman Akihiro Ishikawa.

The quake's focus was 48 kilometers (30 miles) below sea level in the Pacific Ocean off the coast of the town of Kushiro in Hokkaido, 900 kilometers (560 miles) north of Tokyo, the Meteorological Agency said.

The latest tremor followed a quake registering 6.8 on the Richter scale in the central region of Niigata on October 23, which killed a total of 40 people and was followed by hundreds of aftershocks that have kept residents on edge.

But unlike in Niigata, where the initial tremor struck only 13 kilometers (nine miles) underground, the damage was limited in Hokkaido thanks to the quake's deep epicenter, a Meteorological Agency official said.

"The focus of the Niigata quake was very shallow, but that of the quake this morning was deeper and that made a big difference in terms of the damage," the official said.

The quake cut off electricity for some 1,580 households in Hokkaido, but a spokesman for Hokkaido Electric Power Co. said power was restored about three hours later.

A total of some 13,000 households in the town of Nemuro were advised to evacuate, but the local government soon lifted the advisory.

The quake set off a tsunami alert that was called off after tidal waves rose to just 10 centimeters (four inches).

An island near Hokkaido was struck in a 1993 earthquake by deadly tidal waves that reached as high as 20 meters (66 feet), contributing to that disaster's death toll of 229 dead or presumed dead.

Damage from last month's Niigata quake was likely to reach three trillion yen (29 billion dollars) with the destruction of infrastructure severely disrupting the economy, officials said.

The Niigata earthquake, which also injured 2,857 people, was the deadliest to strike tremor-prone Japan since 1995, when 6,433 people were killed in the western city of Kobe.

The first Niigata tremor could be felt in Tokyo, where authorities later announced the development of a computer program to help minimize casualties in the event the capital is struck by the long-dreaded "big one."

The computer program can automatically identify areas in which trains and vehicles should not operate when Tokyo is hit by any earthquake above 4.0 on the Richter scale, according to the city government.

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