Tokyo: A magnitude 7.7 earthquake struck off the north-eastern coast of Japan on Monday, prompting authorities to urge residents to stay away from coastal areas where tsunami waves of up to three metres were expected.

Two hours after the tremor, which struck at 4.53 pm (5.53 pm AEST), tsunami waves as high as 80 centimetres had been detected. A tsunami warning was later downgraded to a tsunami advisory.

The quake measured an “upper 5” on Japan’s seismic intensity scale – strong enough to make it difficult for people to move around and cause unreinforced concrete block walls to collapse. The tremor had an epicentre in the Pacific Ocean and was 20 kilometres deep, according to the Japan Meteorological Agency.

There were no immediate reports of casualties or major damage, government spokesperson Minoru Kihara told a news conference as night fell in the capital Tokyo.

Several port towns, including Otsuchi and Kamaishi – both hit hard by a massive earthquake and tsunami in 2011 – earlier issued evacuation orders for thousands of residents, according to public broadcaster NHK. Bullet train services were halted and some motorways were closed following the tremors.

Ships sailed out of Hachinohe port in Hokkaido in anticipation of the waves, footage aired on NHK showed, as a “Tsunami! Evacuate!” alert flashed across the screen.

Prime Minister Sanae Takaichi, who said the government had set up an emergency taskforce, had urged citizens in the affected areas to evacuate to safety.

Following the quake, the government issued a warning of a heightened risk of a megaquake.

Normally, the probability of an earthquake of magnitude 8 or stronger striking along the Japan Trench and Kuril Trench in the Pacific off northern Japan in a week is about 0.1 per cent, but during the week that follows Monday’s quake, it will be higher at around 1 per cent, a government official told a press conference.

“Please take anti-disaster steps, while embracing the idea that one must protect one’s own life,” the official said.

A three-metre tsunami could cause damage to low-lying areas by flooding buildings and carrying off anybody exposed in its currents, according to JMA.

Japan is one of the world’s most earthquake-prone countries. A tremor occurs in the island nation at least every five minutes. Located in the “Ring of Fire” of volcanoes and oceanic trenches partly encircling the Pacific Basin, Japan accounts for about 20 per cent of the world’s earthquakes of magnitude 6.0 or more, such as the 2011 disaster that caused nuclear meltdowns at a Fukushima power plant.

There are no nuclear power plants in operation in the affected areas and Hokkaido Electric Power Co and Tohoku Electric Power Co said there were no abnormalities reported at their idled facilities there.

The International Atomic Energy Agency also said that there had been no abnormalities observed at Japan’s nuclear facilities.

Reuters

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