Japan rocked as quake triggers tsunami near Fukushima site

Coastal residents fled to higher ground as a powerful earthquake sent a series of moderate tsunami toward Japan's northeastern shore Tuesday and fuelled concerns about the Fukushima nuclear power plant destroyed by a much larger tsunami five year ago.

Lines of cars snaked away from the coast in the pre-dawn hours after authorities issued a tsunami warning and urged residents to seek higher ground immediately. The warning was lifted nearly four hours later.

The magnitude 7.4 earthquake struck in the same region that was devastated by a tsunami that followed a much larger magnitude 9.0 quake in 2011, killing some 18,000 people. The US Geological Survey measured Tuesday's quake at 6.9.

At least 12 people were reported injured, and Japanese TV images showed items scattered on the floor in a store, and books that had fallen from shelves in a library. The earthquake shook buildings in Tokyo, 240 kilometres southwest of the epicentre.

In some areas, water could be seen rushing up rivers, which funnel tsunamis to a greater height, but it remained well within flood embankments. It was eerily reminiscent of the 2011 disaster, when much larger tsunamis rushed up rivers and overflowed, wiping away entire neighbourhoods.

The first tsunami waves hit about one hour after the earthquake. The highest one, 1.4 metres in height, reached Sendai Bay about two hours after the quake.

The operator of the Fukushima Dai-ichi plant said there were no abnormalities observed at the plant, though a swelling of the tide of up to 1 meter was detected offshore.

The plant was swamped by the 2011 tsunami, sending three reactors into meltdown and leaking radiation into the surrounding area. The plant is being decommissioned but the situation remains serious as the utility figures out how to remove still-radioactive fuel rods and debris and what to do with the melted reactor cores.

Plant operator TEPCO said a pump that supplies cooling water to a spent fuel pool at the nearby  Fukushima Dai-ni plant stopped working, but that a backup pump had been launched to restore cooling water to the pool.

Both plants are run by Tokyo-based TEPCO.

Naohiro Masuda, head of TEPCO's decommissioning unit, said he believes that the pump was shut off automatically by a safety system as the water in the pool shook.

He said decommissioning work at the destroyed Dai-ichi plant had been temporarily suspended because of the earthquake.

For many, the early morning jolt brought back memories of the 2011 earthquake and tsunami.

Earthquakes are common in Japan, one of the world's most seismically active areas. Japan accounts for about 20 percent of the world's earthquakes of magnitude 6 or greater.

The 11 March 11 2011 quake was magnitude 9, the strongest quake ever recorded in Japan. The massive tsunami it generated knocked out the Fukushima plant, causing the worst nuclear crisis since Chernobyl a quarter of a century earlier.