TOKYO, May 12 (Xinhua) -- An earthquake with a magnitude of 5.2 rocked Japan's Nagano prefecture at 10:29 a.m. local time (0129 GMT), Japan Meteorological Agency (JMA) said Saturday.

The magnitude of the temblor was initially estimated at 5.1 but later upgraded to 5.2.

The temblor was centered in the northern part of Nagano prefecture in central Japan, with the epicenter at a latitude of 36.6 degrees north and a longitude of 137.9 degrees east and at a depth of 10 km.

The earthquake logged lower 5 in some parts of Nagano prefecture on the Japanese seismic intensity scale which peaks at 7.

So far no major damage or injuries were reported, and no tsunami warning has been issued.

Local government said the Kashiwazaki-Kariwa nuclear plant in the neighboring prefecture of Niigata, which was currently not in operation, suffered no damage.

The JMA warned of possible quakes of similar intensity in the following week, especially in the next two or three days.