A tsunami warning was issued by Japanese officials on Wednesday for the prefectures of Miyagi and Fukushima following a 7.3 magnitude earthquake. The warning was later retracted.

The quake struck large parts of eastern Japan, including Tokyo, where buildings shook violently. Some two million people in the most affected areas were without power for much of the evening,  including 700,000 people in the capital.

There were no immediate reports of major damage or casualties, though a high-speed Shinkansen train was derailed. Although none of the 100 passengers were badly hurt, the news was still shocking to Japanese residents due to the train's stellar safety record.

Officials said that the Fukushima nuclear power station was secure, though they warned residents to be wary of powerful aftershocks that could follow in the coming days.

Wednesday's tremor came shortly after the anniversary of a 2011 earthquake and tsunami that killed nearly 20,000 people. That quake, which was of 9.0 magnitude, triggered one of the worst nuclear disasters in modern history.

es/aw (AP, AFP, Reuters)