Nuclear power facilities across Japan are not damaged and there was no radiation leakage, Japan's Prime Minister Naoto Kan told media persons in Tokyo.
Nuclear plants on the Pacific coast in Miyagi and Fukushima prefectures have been automatically shut down Friday following a powerful earthquake that hit a wide area in northeastern Japan, the operators said, the Mainichi Daily News reported.
Tokyo Electric also said it kept operating the Kashiwazaki-Kariwa nuclear plant on the Sea of Japan coast in Niigata Prefecture, while Hokkaido Electric Power Co. reported no problems at its Tomari No. 1, No. 2 and No. 3 plants in the northernmost main island.
There were no immediate signs of any problems at the Hamaoka nuclear plant on the Pacific coast in Shizuoka Prefecture, southwest of Tokyo, the prefectural government said.
Onagawa nuclear power plant in Miyagi Prefecture automatically halted operations following the quake. Its operator, Tohoku Electric Power Co., was checking whether any damage was caused, The Nikkei reports.
A major blackout occurred across a wide area of northeastern Japan.
Massive earthquake followed by a tsunami hit Japan on Friday, with reports of 'numerous' injuries and ships being washed ashore by waves.
Japan's NHK says a small tsunami hit the shore near the epicenter around 3 pm local time.
The Pacific Tsunami Warning Centre in Hawaii said a tsunami warning was in effect for Japan, Russia, Marcus Island and the Northern Marianas.
The quake measuring 8.9 on Richter scale struck about 382 kilometres (237 miles) northeast of Tokyo, the US Geological Survey said.