Tokyo, Japan: A 6.8-magnitude earthquake struck off Japan's northeastern coast on Saturday, authorities said, but no tsunami warning was issued and there were no immediate reports of damage.

The United States Geological Survey (USGS) said the mid-morning quake hit at a depth of 47 kilometres (29 miles) in the Pacific, off Ishinomaki in Miyagi prefecture -- near the epicentre of a huge 2011 quake which triggered a towering tsunami, killing more than 18,000 people.

Japan's meteorological agency said there was no tsunami risk following Saturday's jolt, which produced strong shaking along parts of the eastern coast and was also felt in Tokyo.

"We are still collecting information but have not received any reports of injuries or damage," local government spokesman Tomoki Sawata told AFP, calling the quake "fairly strong".

Local railway firms suspended services, including of shinkansen bullet trains, public broadcaster NHK said, while elevators stopped in some buildings in Miyagi.

Fukushima nuclear plant operator TEPCO said the facility, which melted down in the wake of the 2011 tsunami, did not show any abnormalities after the latest jolt.

"Operations are under way as usual," TEPCO spokesman Koichiro Shiraki told AFP.

Japan sits on the Pacific "Ring of Fire", an arc of intense seismic activity that stretches through Southeast Asia and across the Pacific basin.

The country is regularly hit by quakes, and has strict construction regulations intended to ensure buildings can withstand strong tremors.

In March, a strong 7.2-magnitude earthquake struck off the northeastern coast. Japan's authorities issued a tsunami advisory but there was no damage on the coastline.

The region was also shaken by another strong quake in February that injured dozens. Meteorologists said it was an aftershock of the 2011 quake.