A 5.6-magnitude quake hit western Japan early Monday, injuring five people and damaging buildings and roads, as officials warned stronger tremors could come in the days ahead.
The shallow tremor was gauged as magnitude 5.6 by the US Geological Survey and 6.1 by Japan's meteorological agency on the Richter scale.
It rocked the west of the main island of Honshu, 96 kilometres (60 miles) north of Hiroshima, at 1:32am (1632 GMT Sunday).
The Japanese agency urged residents to stay vigilant.
"We want the areas that experienced strong tremors to be on guard in the coming week or so against quakes that could be as powerful as the upper five," agency official Toshiyuki Matsumori told a news conference, referring to a Japanese seismic scale with a maximum intensity of seven.
An upper five on Japan's Shindo scale refers to tremors that make it difficult to walk without holding onto something.
Strong aftershocks could continue for two to three days, Matsumori said, and several strong tremors have already been felt in the region hit by the initial quake.
Five people were hurt in the quake, including a 17-year-old boy who broke his leg after falling from his bed, but no life-threatening injuries were reported.
Around 100 households lost water in Oda City, prompting troops to send trucks to set up makeshift water supply stations.
Damage to some buildings and roads were also reported.
No problems were reported at the nearby Shimane nuclear power station, which has been offline for a checkup.
Japan sits on the so-called Pacific "Ring of Fire" where a large proportion of the world's earthquakes and volcanic eruptions are recorded.
A devastating magnitude 9.0 quake -- which struck under the Pacific Ocean on March 11, 2011 -- and a resulting tsunami caused widespread damage and claimed the lives of thousands of people.