A powerful earthquake with a magnitude of 7.1 struck Japan's main northern island of Hokkaido early Monday. Authorities say at least 13 people were injured.

The tremor, which hit just after 3:30 in the morning local time, struck a wide area of the country and was felt as far away as Tokyo, some 800 kilometers from the epicenter. Some of the injured say they were hit by falling objects in their homes but there was relatively little damage reported in the mainly rural area nearest the quake.

The earthquake division chief at the Japan Meteorological Agency, Masahiro Yamamoto, said the quake occurred in the Pacific Ocean about 48 kilometers under the surface. Mr.Yamamoto said the area usually gets shaken by earthquakes of magnitude 6.5 or higher about every decade. He says that while aftershocks can be expected, scientists do not believe the area is experiencing any unusual seismic activity.

The quake prompted the agency to issue a tsunami alert for about an hour along Hokkaido's Pacific coastal areas. One such wave measuring ten centimeters high hit about 30 minutes after the quake. Authorities in the city of Nemuro temporarily advised 13,000 households to evacuate to shelters.  Hundreds of homes were without electricity. Train service in parts of Hokkaido was suspended until the tracks could be inspected for damage.

A magnitude 6.8 earthquake, followed by several aftershocks, struck the Niigata area of Japan last month, killing 40 people and damaging 16,000 homes. That was the deadliest quake in the country since 1995 when a magnitude 7.2 tremor killed 6,000 people in the western port city of Kobe.