The quake occurred at 3:32 am (1832 GMT Sunday) with its focus 48 kilometers (30 miles) below sea level in the Pacific Ocean off the coast of Kushiro, Hokkaido, 900 kilometers (560 miles) north of Tokyo, the agency said.

At 3:37 am, the agency issued a tsunami warning for the eastern shores of Hokkaido but lifted it just over an hour later, an agency official said.

A police spokesman in Hokkaido said at least 13 people were injured, including an 80-year-old woman who broke her arm after falling in her house.

"She may have to stay in hospital for at least four weeks but as far as we know, the rest of the (injured) people sustained light injuries," the police spokesman said.

The quake also 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.

Following the initial quake, six aftershocks measuring above 4.0 on the Richter scale shook Hokkaido, a meteorological agency official said.

The latest tremor followed a powerful earthquake in the central Japanese region of Niigata on October 23, which killed a total of 40 people in one of Japan's worst series of quakes in recent memory.

All rights reserved. � 2005 Agence France-Presse. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by Agence France-Presse. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of Agence France-Presse.