One of at least four damaged buildings collapsed and at least five were buried under debris after a 6.8-magnitude quake hit the northern parts of central Japan's Nagano Prefecture at around 10:08 p.m. local time (1308 GMT) Saturday, local reports cited firefighters as saying.
The damage and injuries were reported at Hakuba village in the northern part of the prefecture. Separate reports said at least 10 people were wounded in Hakuba and a building was fully damaged in another village.
The strong quake triggered no tsunami alerts, said Japan's Meteorological Agency. Two moderate aftershocks measured at 4.3- magnitude and 4.1-magnitude occurred.
The epicenter was initially detected at around 36.7 degrees north latitude and 137.9 degrees east longitude, with a depth of 10 km, said the agency.
Japan's public broadcaster NHK said the strong tremor of the M6. 8 quake lasted for about 15 seconds, adding no abnormality was found in a nuclear power plant in neighboring Niigata Prefecture.
The quake triggered black-out in some areas and the power failure has affected Shinkansen bullet train services in the region.
The quake also triggered a landslide in the region which blocked roads. The local fire department is still checking for damage and injuries.