TOKYO (Reuters/AFP) - An earthquake with a preliminary magnitude of 5.6 shook buildings in eastern Japan, including the capital Tokyo, on Tuesday but there were no reports of serious damage.

The earthquake was centred in Ibaraki Prefecture, just north-east of Tokyo, Japan's Meteorological Agency said. The depth of the earthquake was 50km and there was no risk of a tsunami, it added. Seismologists said the epicentre was around 44km north-north-east of the Japanese capital.

Japan Atomic Power Co and Tokyo Electric Power Co (Tepco) reported no irregularities at their three nuclear plants in eastern Japan.

A Japan Atomic official said there have been no irregularities at the 1.1GW Tokai Daini plant, which has been shut since May 2011. A Tepco spokesman said there has been no irregularities at the Fukushima No. 1 nuclear plant, wrecked by the March 2011 quake and tsunami, and Fukushima No. 2 plant, which has been shut since March 2011.

"There was no abnormality in our monitoring at the Fukushima No. 1 nuclear power plant following the earthquake. Also, we have not received any reports of damage from the latest quake," spokesman Keisuke Murakami said.

The US Geological Survey said the quake had a magnitude of 5.6.

An official at the Ibaraki prefectural government said checks were ongoing, but that so far there appeared to be nothing amiss in the wider area.

"We have not received any reports of damage, injuries or casualties following the earthquake. We are still checking if the quake could result in damage," he said.

Japan is hit by around a fifth of the world's powerful quakes every year and sits at the conjunction of several tectonic plates.

Building codes are rigorous and regular disaster drills are held, helping to ensure that despite their frequency and their violence, quakes usually pass without loss of life or significant damage to property in Japan.

However, the 9.0-magnitude undersea quake of March 2011 sparked a huge tsunami that smashed into the country's north-east coast, killing around 18,000 people and creating the world's worst nuclear emergency in a generation.