TOKYO (Reuters) - A magnitude 6.3 earthquake shook buildings in Japan's capital of Tokyo on Tuesday, the U.S. Geological Survey (USGS) and witnesses said.

The quake was initially reported at a magnitude of 6.2 off the northeast coast of the main island of Honshu at a depth of 20.5 miles, the USGS said.

Japan broadcaster NHK said there was no threat of a tsunami and the U.S. Pacific Tsunami Warning Center also said there was no danger of a tsunami.

(Reporting by Reuters staff)