Nuclear power plants in the region were conducting safety checks, public broadcaster NHK said.
A powerful earthquake struck off Japan’s northern coast on Monday, triggering a tsunami alert, the Japanese Meteorological Agency said.
The agency said the magnitude 7.2 quake struck off Hokkaido, near the coastal city of Aomori with an epicentre about 50 kilometres below the surface of the sea.
The agency, which had previously issued a tsunami alert warning of waves up to three metres, said a tsunami of 40 centimetres had struck the Hokkaido prefecture town of Urakawa and the Aomori prefecture port of Mutsu Ogawara.
Nuclear power plants in the region were conducting safety checks, public broadcaster NHK said.
Japanese Prime Minister Sanae Takaichi, in brief comment to reporters, said the government set up an emergency task force to urgently assess the extent of damage.
"We are putting people's lives first and doing everything we can," she said.
This is a developing story and our journalists are working on further updates.