A 6.9-magnitude earthquake followed by a 7.1 aftershock struck off Japan's southern island of Kyushu on Thursday, the United States Geological Survey said.
Tsunamis of up to one metre were expected to arrive or have arrived in some coastal areas in Kyushu and Shikoku islands, broadcaster NHK reported.
The first quake struck at a depth of 33 kilometres (20 miles) followed by a second one nearby at a depth of 25 kilometres, the USGS said.
The Japanese government set up a special task force in response to the quakes, according to a statement.
Sitting on top of four major tectonic plates along the western edge of the Pacific "Ring of Fire", Japan is one of the world's most tectonically active countries.
The archipelago, home to around 125 million people, experiences around 1,500 jolts every year and accounts for around 18 percent of the world's earthquakes.
The vast majority are mild, although the damage they cause varies according to their location and the depth below the Earth's surface at which they strike.
Still, even large quakes usually cause little damage thanks to special construction techniques and strict building regulations in the world's number four economy.
On New Year's Day, at least 260 people died after a massive earthquake hit the peninsula, including 30 "quake-linked" deaths as well as those killed directly in the disaster.
The January 1 quake and its aftershocks toppled buildings, caused fires and knocked out infrastructure at a time when families were celebrating the new year.
