Japan has issued a tsunami warning after a major 7.2-magnitude quake struck the main Honshu island, swaying buildings in the capital Tokyo. The Japan Meteorological Agency, said the tremor struck 10 kilometres below the sea floor, and issued a tsunami warning for Honshu's Pacific coast, including Iwate, Miyagi and Fukushima prefectures. There are no immediate reports of any damage or casualties. Tsunami waves are anticipated to be around 50 centimetres high, the agency said, adding it expected no major damage. Nuclear power operators Tokyo Electric and Tohoku Electric said their atomic plants in Aomori, Miyagi and Fukushima prefectures are safe. Some bullet trains in the region automatically stopped when the quake hit and later resumed services, railway operators said.