A powerful earthquake, with a preliminary magnitude of M7.3 on the Richter scale, since reduced to M6.9  by the USGS, struck Japan 156 miles northeast of Tokyo at 5:59am local time.

The epicenter of the earthquake, which was felt in Tokyo, was off the coast of Fukushima prefecture at a depth of about 10 km, Japan's Meteorological Agency said, the same Fukushima that was site of the 2011 natural disaster and tsunami that resulted in the worst nuclear power plant disaster since Chernobyl.

There were no immediate reports of damage or injury, Reuters notes. Tokyo Electric Power Co was checking its nuclear plants in Fukushima for damage, public broadcaster NHK said.  Tohoku Electric Power Co said there was no damage to its Onagawa nuclear plant.

Television footage showed ships moving out to sea from Fukushima harbors, as the meteorological agency warned of a tsunami of 3 meters (10 feet) for Fukushima, where Tepco's Daiichi nuclear plant was devastated in a March 2011 quake and tsunami.

The March 11, 2011, quake was magnitude 9, the strongest quake in Japan on record. The massive tsunami it triggered caused world's worst nuclear crisis since Chernobyl a quarter of a century earlier. The U.S. Geological Survey initially put Tuesday's quake at a magnitude of 7.3 but down graded it to 6.9.

All nuclear plants on the coast threatened by the tsunami are shutdown in the wake of the Fukushima disaster. Only two reactors are operating in Japan, both in the southwest of the country. Even when in shutdown nuclear plants need cooling systems operating to keep spent fuel cool.

NHK also adds that a tsunami, as high as 3 meters, has been detected at Fukushima