Japanese authorities say at least 23 people were injured following a powerful 7.5 magnitude earthquake off northern Japan late on Monday, further warning of possible aftershocks and an increased risk of a megaquake.

A tsunami wave of up to 70 centimetres was measured in Kuji port in Iwate prefecture, just south of Aomori, and tsunami levels of up to 50 centimetres struck other coastal communities in the region, the Japan Meteorological Agency said, but all tsunami warnings were lifted on Tuesday morning.

The temblor struck at about 11.15 pm in the Pacific Ocean, around 80 kilometres off the coast of Aomori, the northernmost prefecture of Japan’s main Honshu island.

“I’ve never experienced such a big shaking,” convenience store 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.

The Fire and Disaster Management Agency said 23 people were injured, including one seriously. Most of them 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 quake's magnitude as 7.5, down from its earlier estimate of 7.6.

Some 2,700 homes in Aomori were without power, according to Kyodo news agency, and there were numerous reports of fire.

The quake was also felt in the northern hub of Sapporo, where alarms rang on smartphones to alert residents.

A reporter for NHK in Hokkaido described a horizontal shaking of around 30 seconds that made him unable to remain standing as the earthquake struck.

With the quake rattling much of northern Japan, Shinkansen bullet-train service was suspended between Fukushima and Aomori, with the operator posting online that some service was expected to resume later on Tuesday morning.

Chief Cabinet Secretary Minoru Kihara said nuclear power plants in the region were conducting safety checks.

The Nuclear Regulation Authority said about 450 litres of water spilled from a spent fuel cooling area at the Rokkasho fuel reprocessing plant in Aomori, but that its water level remained within the normal range and there was no safety concern.

The meteorological agency issued a caution about possible aftershocks in the coming days.

It said there is a slight increase in risk of a magnitude 8-level quake and possible tsunami occurring along Japan's northeastern coast from Chiba, just east of Tokyo, to Hokkaido.

The agency urged residents in 182 municipalities in the area to monitor their emergency preparedness in the coming week.

Prime Minister Sanae Takaichi said in brief comments to reporters that 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.

Later, she urged residents in the region to pay attention to the latest information from local municipalities.

“Please be prepared so you can immediately evacuate as soon as you feel a tremor."

The quake struck about 80 kilometres northeast of Hachinohe, and about 50 kilometres below the sea surface, the meteorological agency said.

It was just north of the Japanese coast that suffered the magnitude 9.0 quake and tsunami in 2011 that killed nearly 20,000 people and destroyed the Fukushima Daiichi nuclear power plant.

“You need to prepare, assuming that a disaster like that could happen again," the meteorological agency's earthquake and volcano division official Satoshi Harada said. (AP/AFP)