An earthquake with a preliminary magnitude of 4.4 shook buildings in Tokyo today.
Fire department officials said there were no reports of damage or injuries. No tsunami warning was issued.
The quake was centred in Ibaraki prefecture, slightly north of Tokyo, and the focus was at a depth of 40 km (25 miles).
In late March, a strong earthquake in central Japan killed one person, injured more than 200 and caused widespread damage.
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Japan is one of the world's most earthquake-prone nations. A tremor occurs at least once every five minutes, and each year there are up to 2,000 quakes that can be felt by people.