A strong earthquake jolted Japan's northeast coast on Wednesday, shaking buildings, leaving parts of Tokyo without power and triggering a tsunami warning.

The tremor registered magnitude 7.3 and as high as a 6-plus on the Japanese shaking intensity scale in some areas - too strong for people to stand, according to public broadcaster NHK.

Prime Minister Fumio Kishida said the government was working to assess the extent of any damage after the tremor.

The same region was hit by a major quake followed by a tsunami in 2011 that triggered the Fukushima nuclear disaster.

Tokyo Electric Power Company (9501.T) said that around 2 million households were without power and that it was checking the condition of reactors at the Fukushima plant, NHK said.

Authorities warned residents in Fukushima, Miyagi and Yamagata prefectures to expect after shocks.