The epicentre of the earthquake was located in northern Ibaraki at a depth of 60 kilometres (37 miles).
The intensity of the aftershocks reacheda number four under Japan's seven-score scale.
No tsunami alert has been declared. There is also no information about any damage and victims caused by the earthquake.
There were no abnormal situations in connection with the earthquake at the Tokai-2, Fukushima-1, and Fukushima-2 nuclear power plants (NPPs), NHK reported, citing the operators of the NPPs.