The Japan Meteorological Agency initially said a tsunami as high as 3 metres could hit Japan's northeastern coast after the earthquake struck off the coast late on Monday.
Tsunami warnings were issued for the prefectures of Hokkaido, Aomori and Iwate, and tsunamis from 20 to 70 cm high were observed at several ports, the agency said.
In the early hours of Tuesday, the agency downgraded the warnings to advisories, meaning it now sees lower estimated wave heights and less risk of inundation.
The epicentre of the quake was 80 km off the coast of Aomori prefecture, at a depth of 50 km, the agency added.
"There have been seven injuries reported," Prime Minister Sanae Takaichi told reporters early on Tuesday morning.
Takaichi said the government is urgently assessing the extent of damage.
On Japan's 1-7 scale of seismic intensity, the tremor registered as an "upper 6" in Aomori prefecture -- a quake strong enough to make it impossible to keep standing or move without crawling.
In such tremors, most heavy furniture can collapse and wall tiles and windowpanes are damaged in many buildings.
East Japan Railway suspended some services in the area, which was also hit by the massive 9.0-magnitude quake in March 2011.
There is little information of major damage, according to public broadcaster NHK. It cited a hotel employee in Hachinohe as saying several people were injured and taken to a hospital, but that all were conscious.
"There is a possibility that further powerful and stronger earthquakes could occur over the next several days," an agency official said at a briefing.
No irregularities were reported at nuclear power plants in the region run by Tohoku Electric Power and Hokkaido Electric Power, the utilities said.
Japan is one of the world's most earthquake-prone countries, with a tremor occurring at least every five minutes.
Located in the "Ring of Fire" of volcanoes and oceanic trenches partly encircling the Pacific Basin, Japan accounts for about 20 per cent of the world's earthquakes of magnitude 6.0 or greater.
The northeastern region suffered one of the country's deadliest earthquakes on March 11, 2011, when a 9.0-magnitude tremor struck under the ocean off the coast of the northern city of Sendai.
It was the most powerful ever recorded in Japan and set off a series of massive tsunamis that devastated a wide swathe of the Pacific coastline and killed nearly 20,000 people.
The 2011 tsunami also damaged the Fukushima Daiichi nuclear plant, leading to a series of explosions and meltdowns in the world's worst nuclear disaster for 25 years.
with Reuters
