A magnitude 7.1 earthquake struck southern Japan early on Saturday, triggering a tsunami advisory, though it was later lifted and no irregularities were reported at three nuclear power plants in the area, media reported.
There were no immediate reports of casualties in the quake, the epicentre of which was near the city of Kumamoto and measured at a depth of 40 km (25 miles), the U.S. Geological Survey said.
A quake in the same region of 6.4 magnitude on Thursday evening killed nine people and injured at least 1,000.
"Thursday's quake might have been a foreshock of this one," Shinji Toda, a professor at Tohoku University, told national broadcaster NHK.
The Japan Meteorological Agency said the quake was 7.1 magnitude and it initially issued a tsunami advisory, which identifies the presence of a marine threat and asks people to leave coastal regions, for the Ariake and Yatsushiro seas.
NHK said the advisory suggested a possible wave of one metre in height. The advisory was later lifted.
NHK quoted an official at a hospital near the epicentre as saying it had lost power after the Saturday quake and had to use its generators.
A magnitude 9 quake in March 2011, to the north of Tokyo, touched off a massive tsunami and nuclear meltdowns at Fukushima. Nearly 20,000 people were killed in the tsunami.
(Reporting by Tokyo bureau; Writing by John Stonestreet; Editing by Robert Birsel)
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