A big quake off Japan injured at least 30 people, authorities said Tuesday, damaging roads and knocking out power for thousands in freezing temperatures.

The Japan Meteorological Agency said the magnitude 7.5 quake at 11:15 pm on Monday (1415 GMT) -- downgraded from its first reading of 7.6 -- raised the chances of similar or larger tremors in the coming days.

Prime Minister Sanae Takaichi said 30 people were injured in the quake off the coast of the northern Aomori region, which triggered tsunami waves up to 70 centimetres (28 inches).

Daiki Shimohata, 33, a civil servant in Hashikami on Honshu island, told AFP that he and his family rushed outside their home.

"The tremor was something that we've never experienced. It lasted maybe for about 20 seconds," Shimohata said by phone.

"We w

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