A powerful earthquake off the northeast coast of Japan shook a large area late Thursday.  The jolt appeared to be an aftershock from the catastrophic earthquake and tsunami that hit Japan nearly four weeks ago.

The earthquake generated a tsunami warning, and Japan's NHK television immediately warned residents in the area to move to higher ground, but there were no immediate reports of major disruptions in the ocean.

The earthquake and tsunami alert raised fears about possible effects at the damaged Fukushima nuclear reactor, which has been leaking radio since the original earthquake.