A tsunami of 80cm was observed at Kuji port in Iwate Prefecture following the magnitude 7.4 earthquake off the Sanriku coast on April 20, with waves of up to 3m forecast for Pacific coastlines of Hokkaido and northern Japan, the Yomiuri Shimbun reported.

Japan's Meteorological Agency issued tsunami warnings for the central Pacific coast of Hokkaido, the Pacific coast of Aomori Prefecture and Iwate Prefecture. Lower-level tsunami advisories were issued for the eastern and western Pacific coasts of Hokkaido, the Sea of Japan coast of Aomori, Miyagi and Fukushima prefectures.

The first wave at Miyako in Iwate Prefecture was observed at 17:10 local time, with the maximum wave so far reaching 40cm at 17:21. A first wave was also recorded at Kamaishi at 17:19, with the maximum wave still being measured.

At Ofunato, the first wave was observed at 17:10 with the maximum still being measured. The 80cm reading was registered at Kuji port at 17:34, after the first wave arrived at 17:26.

Tsunami activity has also been recorded offshore. Off Aomori at 50km from the coast, the first wave arrived at 17:06 with the maximum still being measured. Off Iwate at 60km, the first wave arrived at 16:59. Off Miyako in Iwate, the first wave arrived at 17:04.

Forecast wave heights remain at 3m for the central Pacific coast of Hokkaido, Pacific coast of Aomori and Iwate Prefecture, with 1m forecast for the eastern and western Pacific coasts of Hokkaido, the Sea of Japan coast of Aomori, Miyagi and Fukushima.

The Japan Meteorological Agency has urged residents in warning areas to evacuate immediately to higher ground.

The Sanriku coast was the area most severely affected by the March 2011 Great East Japan Earthquake and tsunami that killed more than 18,000 people and triggered the Fukushima Daiichi nuclear disaster.