An earthquake preliminarily measured at 5.6 magnitude has hit off the Japanese coast, just north of Tokyo, Japanese national broadcaster NHK reports.
Local news outlets say the quake was felt in the Saitama and Tokyo areas, with buildings swaying.
Metro operations were briefly suspended on all routes in Tokyo, but services restarted four minutes later.
An elevator maintenance firm in Tokyo said several elevators stopped in the metropolitan area due to the quake with commuters asked to "use emergency buttons," according to NHK.
TASS news agency reports that books fell from shelves and furniture shook at its headquarters in Tokyo.
No damage was reported at airports, the Japan Times reports, citing officials.
However, NHK claims there was some panic just after the tremors when windows shook at a hotel where a G7 Science and Technology ministerial entourage is staying ahead of a conference this week.
A 5.6 quake is considered strong according to the Japanese 7-point scale. NHK reports there was no immediate tsunami warning, however.
Japan Nuclear Power Association says a reactor at Tokai Nuclear Plant in Tokai village has "suspended operation" due to the quake. Tokyo Electric Power reports no incidents at the plant.
The Japanese meteorological society confirmed the reports of a 5.6 strong earthquake. It said the epicenter of the shocks was in the prefecture of Ibaraki.
No information of damage or casualties has been reported from the Ibaraki prefecture.
Meanwhile, the US Geological Survey has reported a 5.4 earthquake some 6km west of Iwai.
The Japanese Meteorological Agency says the depth of the quake was estimated at around 40km.
This comes exactly a month after a devastating quake hit the Japanese city of Kumamoto on the island of Kyushu, with 200 aftershocks rocking the country following the initial tremor of 6.5 magnitude. Forty-nine people lost their lives in the tragedy, with some 110,000 people being evacuated from areas close to the epicenter.
Earthquakes are common in Japan, as the country is part of the seismically active "Ring of Fire," stretching from the South Pacific islands to Indonesia, Japan, across to Alaska, and down the west coast of the Americas.
In March 2011, a quake measuring a magnitude of 9 on the international scale hit northern Japan, triggering a tsunami. It caused the meltdown of nuclear reactors at the Fukushima Daiichi nuclear plant, resulting in the world's worst nuclear crisis since Chernobyl.