The Saturday quake triggered a tsunami advisory, though it was later lifted and no irregularities were reported at three nuclear power plants in the area, Japanese media reported.
There were no immediate reports of casualties in the Saturday quake though there were several reports of damage, including some collapsed buildings and cracked roads.
The epicenter of the quake was near the city of Kumamoto and measured at a shallow depth of 10 km, the U.S. Geological Survey said.
The quake on Thursday evening in the same region was of 6.4 magnitude.
“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 Saturday 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 meter in height. The advisory was later lifted.
Several aftershocks rattled the region later on Saturday, including one of 5.8 magnitude.
NHK quoted an official at a hospital near the epicenter as saying it had lost power after the Saturday quake and had to use its generators.
Most of the casualties in the Thursday quake came in the town of Mashiki, near the epicenter, where several houses collapsed.
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.