Tokyo- A powerful earthquake with an estimated magnitude of 5.6 on the open-ended Richter scale jolted the central Japan prefecture of Nagano on Sunday morning, injuring several people.

The temblor, which struck around 7:02 a.m. (10:02 p.m. Saturday GMT), registered upper 5, the fourth-highest level on the 10-notch Japanese seismic intensity scale of 7, in the town of Kiso and the neighboring village of Otaki in the prefecture, according to the Japan Meteorological Agency.

The quake, whose focus was located at a depth of 7 kilometers in the southern part of the inland prefecture, did not cause tsunami, the agency said.

Two more quakes, with their focuses in southern Nagano, occurred around 9:24 a.m. and 3:17 p.m., measuring 4 on the Japanese scale in municipalities including Kiso, the agency said.

According to the Nagano prefectural government, a total of 24 buildings in areas including Kiso suffered partial damage, such as fallen roof tiles and broken windows.

Two prefectural and three municipal roads were closed to traffic due to fallen rocks or cracks. Some sections of the roads were reopened later.

A woman in her 80s was injured on the head by a falling object at her home in Otaki, local fire authorities said. Her injury is believed to be minor.

In Kiso, a woman in her 60s suffered a minor injury, with her right leg caught between a falling chest of drawers and the floor.

The meteorological agency warned that aftershocks measuring up to upper 5 on the Japanese seismic scale could hit areas shaken hard by Sunday's quakes in the next week. The risk of landslides is increasing, the agency also said.

Bullet trains on the Tokaido Shinkansen Line made emergency stops between Kakegawa Station in Shizuoka Prefecture, south of Nagano, and Shin-Yokohama Station in Kanagawa Prefecture, east of Shizuoka, according to Central Japan Railway Co. better known as JR Tokai.

The train service was resumed 10 minutes later, after safety was confirmed. Three trains on the Shinkansen line suffered delays, affecting a total of about 1,600 passengers.

The quakes caused no problem to the two reactors at Hokuriku Electric Power Co.'s Shika nuclear power station in Ishikawa Prefecture, central Japan, according to the power supplier. The No. 1 and No. 2 reactors are offline at present. (Jiji Press)