An earthquake has jolted northwestern Japan, and officials are warning of a tsunami of up to one metre high along parts of the coast.

Japan’s Meteorological Agency said the quake Tuesday night registered a 6.8 magnitude and was located off the western coast of Yamagata — about 50 kilometres southwest of the city of Sakata.

It said the quake’s epicentre was fairly shallow, about 10 kilometres below the sea’s surface. Shallow quakes tend to cause more damage on the Earth’s surface.

The agency predicted a tsunami as high as one metre along the coast of the northwestern prefectures of Yamagata, Niigata and Ishikawa.

All seven reactors at the Kashiwazaki-Kariwa nuclear plant in Niigata were offline and no abnormalities were reported.  Kyodo News agency said service was suspended on two bullet train lines to check for damage.

Reports of the earthquake’s strength ranged from 6.4 to 6.8 depending on the agency, while the U.S. National Tsunami Warning Centre said a tsunami was not expected for British Columbia, Washington, Oregon, California or Alaska.

Japan is one of the most earthquake- and tsunami-prone areas in the world. On March 11, 2011, a 9.0 magnitude offshore quake hit the northeast coast, causing a tsunami that took more than 18,000 lives and triggered a nuclear disaster at the Fukushima power plant.