TOKYO (AP) _ An earthquake registering 5.5 on the Richter scale shook parts of southern Japan early today, injured three people and briefly disrupted train services.

The Central Meteorological Agency said the epicenter of the earthquake was about six miles underground in northern Yamaguchi prefecture on the extreme southwestern tip of the Japanese main island of Honshu.

The Kyodo News Agency quoted police officials in Yamaguchi city as saying that one woman was injured by a falling mirror and two other people received minor injuries. Yamaguchi is about 500 miles southwest of Tokyo.

Kyodo said service on one local train line was stopped to check for damages to the tracks. There were no other reports of damages.

The Richter scale measures the magnitude of a quake by the ground motion recorded on seismographs. An earthquake of 6 on the scale is capable of causing widescale damage near its center.