A magnitude-6.8 earthquake hit northern Japan on Tuesday, shaking buildings as far away as Tokyo and triggering a tsunami warning, broadcaster NHK reported.
Japan sits at the juncture of four tectonic plates - or moving slabs of the earth's outer crust - and is one of the world's most quake-prone regions.
A magnitude-6.0 quake shook the Tokyo area on July 23, injuring more than two-dozen people and suspending flights and trains for hours. A magnitude-5 quake can damage homes and other buildings if it is centred in a heavily populated area.