More than 1,000km of Japan’s eastern seaboard was placed on tsunami alert on Wednesday night as a massive earthquake struck off the coast of the northern island of Hokkaido.

The 8.1 magnitude quake hit at around 8.15pm local time in an area 390km away from the island of Etorofu – one of four islands whose sovereignty is a subject of bitter and long-standing dispute between Japan and Russia.

By international standards, any quake above a 7.0 is treated as creating a significant risk to life and property. The massive undersea quake that caused the devastating Indonesian tsunami of 2004 measured 9.1.

The Japan Meterological Agency predicted tsunamis of up to 2m would hit coastal defences throughout the night, and ordered thousands to evacuate their homes as a precaution. No casualties were reported after the initial tsunami reached the shore around 55 minutes after the original quake was detected. Two smaller tsunamis of between 40cm-50cm later struck the towns of Kushiro and Nemuro, but caused no reported damage.

The tsunami warning was issued as far south as Tokyo, but was not expected to pose a risk to residents or affect commercial shipping. Unlike many parts of South East Asia, Japan has spent years developing an early warning system for tsunamis and has peppered its coast with barrages of “tetrapods” – large concrete breakwaters designed to protect ports and low-lying parts of the coast from tsunamis.

More than 1,200 households along the Hokkaido coast were ordered to evacuate, and to seek higher ground – emergency measures practiced annually in drills held throughout Japan.

Etorofu island is a sparsely populated, outlying part of the Japanese archipelago but is well known to most Japanese for its role in a long-running squabble between Moscow and Tokyo. The islands are known as the Northen Territories to Japanese, but as the Kurile Islands to Russians, whose troops occupied them in the aftermath of the second world war.

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