There were no fears of tsunami waves resulting from the quake which occurred at 8:44 pm (1144 GMT) and lasted a few minutes, the Japan Meteorological Agency said, and there were no immediate reports of casualties or property damage.

The epicenter of the quake was located off the Pacific coast of Ibaraki prefecture, some 150 kilometers (90 miles) northeast of Tokyo, the agency said. Its focus was about 40 kilometers (25 miles) below sea.

The experimental nuclear reactor in Tokai Mura, near the epicenter, shut down on impact as it is progammed to do, a spokesman for the government-backed Japan Atomic Energy Agency said.

It would be re-started manually after safety checks, according to the spokesman, Shinichi Nishikawa.

"The building rolled for 40 seconds or so but no objects fell from shelves or racks," he said.

Some night train runs, including those on the super-fast bullet-train services, were temporarily halted for checks on rails, the public broadcaster NHK reported.

The two runways at Narita airport outside Tokyo were closed for about 10 minutes for checks, airport officials said.

Japan endures 25 percent of the world's major earthquakes and has built its infrastructure accordingly, with Tokyo's high-rises designed to withstand powerful tremors.