An earthquake with a preliminary magnitude of 5.6 shook Tokyo and surrounding areas on Monday, but no tsunami warning was issued, the Japan Meteorological Agency said.
The quake was centred in Ibaraki prefecture just northeast of the Japanese capital. There were no immediate reports of damage or injuries, and no reports of abnormalities at any nuclear facilities.
The US Geological Survey measured the quake at 5.3 magnitude.
The tremor shook buildings in Tokyo and briefly halted some train lines, including the Tokyo Metro subway lines.

Narita airport closed both runways for checks shortly after the quake, but the capital's Haneda airport was operating as normal.
On March 11, 2011, Japan - one of the world's most seismically active nations - was hit with a massive earthquake and tsunami that left nearly 20,000 people dead and set off meltdowns at the Fukushima Dai-ichi nuclear plant.