Around 30 earthquakes, one of them magnitude 6.2, rocked a volcanic island south of Tokyo Wednesday and another significant quake hit the northeast of the country, the national meteorological agency said.
The biggest tremor shook Miyake Island, which lies 175 kilometres (110 miles) south of Tokyo, at around 5:57 pm (0857 GMT). Its depth was 20 kilometres and there was no risk of a tsunami, the Japan Meteorological Agency said.
"There may be slight changes in the level of sea along Japan's coast but there is no fear of damage resulting from this quake," it added.
The volcano erupted in 2000, forcing all 3,800 islanders to evacuate. Many of them have since returned to the island.
According to the agency there have not been any signs of increased volcanic activity.
Tremors were felt across a wide area, including Tokyo, where police said three people had suffered minor injuries.
The authorities on Miyake reported that landslides had blocked some roads.
In Tokyo, the Prime Minister's office set up a committee to monitor the situation.
Later Wednesday a 5.8 magnitude earthquake with a depth of 60 kilometres was felt in Japan's northeast, off the coast of Miyagi prefecture -- the area worst hit by the tsunami of March 2011.
The quake hit at 9.03 pm local time (12.03 GMT), the meteorological agency said, and was felt across a large part of the northeast.
At least one person suffered minor injuries, according to local media.
There were no immediate reports of further damage in Fukushima and Onagawa, which were devastated in 2011.
Tokyo Electric Power Co said no abnormalities had been reported at its Fukushima Daiichi and Daini nuclear power plants, according to Kyodo news agency.
Fukushima was the site of the worst nuclear crisis in a generation triggered by the 2011 tsunami -- reactors went into meltdown and spewed radiation over a wide area, forcing tens of thousands of people from their homes.