TOKYO -- A strong quake measured at 6.8 magnitude hit Japan's Nagano Prefecture at around 10:08 pm local time Saturday, without triggering tsunami alerts, according to Japan's NHK.

The epicenter was initially detected at 36.7 degree north latitude, 137.9 degree east longitude, with a depth of 10 km, said Japan's Meteorological Agency.

The quake was registered at lower 6 of Japan's seismic scale of 7 in parts of the prefecture, said the agency.

As of now, there are no reports on damage and injuries. NHK said the strong tremor lasted about 15 seconds.