A powerful 7.5-magnitude earthquake struck off northern Japan late Monday, injuring more than 20 people and triggering a tsunami of up to 70cm (28 inches) in Pacific coast communities, officials said.

The Japanese government was still assessing damages from the tsunami and late-evening earthquake, which struck at about 11.15pm local time in the Pacific Ocean around 80km (50 miles) off the coast of Aomori, the northernmost prefecture of Japan’s main Honshu island.

“I’ve never experienced such a big shaking,” shop owner Nobuo Yamada told the public broadcaster NHK in the Aomori prefecture town of Hachinohe, adding that “luckily” power lines were still operating in his area.

A tsunami of 70cm (27.5 inches) was measured in Kuji port in Iwate prefecture, just south of Aomori, and tsunami levels of up to 50cm struck other coastal communities in the region, the Japan Meteorological Agency said.

The Fire and Disaster Management Agency said 23 people were injured, including one seriously. Most of the victims were hit by falling objects, NHK reported, adding that several people were injured in a hotel in Hachinohe and a man in Tohoku was slightly hurt when his car fell into a hole.

The meteorological agency reported the earthquake’s magnitude as 7.5, down from its earlier estimate of 7.6. It issued an alert for potential tsunami surges of up to 3 metres (10 feet) in some areas and later downgraded it to an advisory.

AloJapan.com