Tokyo: A magnitude 6.1 earthquake struck off Hokkaido in northern Japan on Saturday night, the US Geological Survey and the Japan Meteorological Agency said.
No tsunami warning was issued after the offshore quake, which shook the coastal cities of Kushiro and Nemuro.
Major Japanese media outlets carried no immediate reports of damage or injuries.
The quake hit at 10:27 pm (1327 GMT) at a depth of around 43 kilometres (27 miles), the USGS said.
An expert speaking on public broadcaster NHK warned residents to be vigilant against quakes for about a week.
Earthquakes are common in Japan, which sits on the Pacific "Ring of Fire", an arc of intense seismic activity that stretches through Southeast Asia and across the Pacific basin.
The country has strict construction regulations intended to ensure buildings can withstand strong earthquakes, and routinely holds emergency drills to prepare for a major jolt.
