A magnitude-6.8 earthquake has struck off the coast of Japan's main island of Honshu, the US Geological Survey says.

There was no threat of a tsunami from the earthquake, the Pacific Tsunami Warning Centre said.

The USGS said the quake's epicentre was located 119 kilometres south-east of Morioka city, at a depth of 39 kilometres.

It originally reported the earthquake as measuring 6.9 on the magnitude scale.

Reuters