A strong earthquake with an estimated magnitude of 4.1 on the open-ended Richter scale hit central Nagano Prefecture on Wednesday morning, the Meteorological Agency said.
There were no immediate reports of any damage or casualties, and no tsunami warnings were issued, agency officials said. The quake struck at about 9:40 a.m., registering 4 -- on the Japanese intensity scale of 7 -- in Kamikochi, and 1 in the neighboring regions of Suwa, Kamioka and Omachi, according to the agency.
The agency estimated the focus of the quake was 10 km underground in central Nagano Prefecture. Two minor quakes followed at 9:46 a.m. and 10 a.m. in the same region, registering 2 and 1 on the Japanese scale, respectively , the officials said.