Witnesses reportedly saw buildings shaking in downtown Tokyo after a 6.9 magnitude earthquake struck southern Japan. For now, there is no threat of a tsunami, and there were no reported irregularities at the Fukushima nuclear power plant.
UPDATE: From Reuters:
There were no immediate reports of injuries or damage and no tsunami warning was issued. The U.S. Geological Survey measured the quake with a magnitude of 6.5.
The quake was measured 400 km (250 miles) below the earth's surface about 580 km (360 miles) south of Tokyo, NHK said. Witnesses said it was felt along much of Japan's east coast.