A powerful earthquake has jolted northwestern Japan, and officials are warning of a tsunami of up to one meter (3.3 feet) high along parts of the coast.

Japan's Meteorological Agency said the quake Tuesday night registered magnitude 6.8 and was located off the western coast of Yamagata about 50 kilometers (30 miles) southwest of the city of Sakata.

It said the quake's epicenter was fairly shallow, about 10 kilometers (6 miles) 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 1 meter (yard) along the coast of the northwestern prefectures of Yamagata, Niigata and Ishikawa.

All seven reactors at the Kashiwazaki-Kariwa nuclear plant in Niigata were off line and no abnormalities were reported.