A powerful earthquake hit northern Japan early on Tuesday, briefly disrupting the cooling functions of a nuclear plant and generating a small tsunami in the Fukushima region that was devastated by a 2011 quake, tsunami and nuclear disaster.
The magnitude 7.4 earthquake, which was felt in Tokyo, sent thousands of residents fleeing for higher ground as dawn broke along the northeastern coast.
There were no reports of deaths or serious injuries hours after the quake hit at 5:59 a.m. It was centred off the coast of Fukushima prefecture at a depth of about 10 km, the Japan Meteorological Agency (JMA) said.
A wave of up to 1.4 metres (4.5 feet) high was recorded at Sendai, about 70 km (45 miles) north of Fukushima, with smaller waves hitting ports elsewhere along the coast, public broadcaster NHK said.
Television footage showed ships moving out to sea from harbours as tsunami warnings wailed after alerts of waves of up to 3 metres (10 feet) were issued.
“We saw high waves but nothing that went over the tidal barriers,” a man in the city of Iwaki told NTV television network.
Aerial footage showed tsunami waves flowing up rivers in some areas, and some fishing boats were overturned in the port of Higashi-Matsushima before the JMA lifted its warnings.
The U.S. Geological Survey measured Tuesday's quake at magnitude 6.9, down from an initial 7.3.
All Japan's nuclear power plants in the area were shut down in the wake of the March 2011 disaster, which knocked out the cooling systems of the Tokyo Electric Power Co's Fukushima Daiichi nuclear plant, causing reactors to melt down and spew radiation into the air, soil and sea.
The cooling system of a storage pool for spent nuclear fuel at the reactor at the Fukushima Daini Plant was initially halted on Tuesday, said a spokeswoman of the Tokyo Electric Power Company, known as Tepco, but was restarted soon after.
Only two reactors are operating in Japan, both in the southwest. Nuclear plants need cooling systems operating even when in shutdown to keep spent fuel cool.
Tohoku Electric Power Co said there was no damage to its Onagawa nuclear plant, while the Kyodo news agency reported there were no irregularities at the Tokai Daini nuclear plant in the Ibaraki prefecture.
Japanese Minister for Disaster Management Jun Matsumoto told reporters there were no reports of significant injuries. One woman suffered cuts to her head from falling dishes, Kyodo reported, citing fire department officials.
Japan accounts for about 20 per cent of the world's earthquakes of magnitude 6 or greater.
The March 11, 2011 quake was magnitude 9, the strongest quake ever recorded in Japan. The massive tsunami it generated knocked out the Fukushima Daiichi plant, causing the worst nuclear crisis since Chernobyl a quarter of a century earlier.
