Thousands of tonnes of soil and rock crashed through villages and across highways, severing transport links and crushing houses as people slept.
At least 41 people died in the double disaster, many killed by falling debris as yesterday's 7.0 magnitude quake finished off what a smaller tremor had started late Thursday.
Others suffocated when torrents of earth buried their homes.
From the air, the scale of the devastation becomes apparent; huge hillsides just gave way and great fissures opened up in the ground, swallowing roads, car parks and buildings.
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Two historic tourist spots suffered -- the 250-year-old main gate of Aso Shrine collapsed, as did a stone wall at Kumamoto castle, a stronghold that survived rebellions and attacks by warring samurai in centuries past.
Traditional-style Japanese houses were the worst hit -- their delicately-curved slate roofs smashed and their wooden frames splintered.
In Mashiki, homes that had been in families for generations were simply ripped apart by the violence the quake unleashed; their upper floors crashing down when cedar-wood support columns snapped.
"I am so glad that we are alive now. That is all," Kenji Shiroshita, 48, told AFP after standing in line for rice and water at the town hall.
Shiroshita said Thursday's initial 6.2 magnitude quake had been frightening in an area unused to the powerful tremors that rattle other parts of Japan.
But the rapid restoration of the power supply had lulled him into a false sense of security.
"I never expected the second one because the electricity was back on and there were cars on the roads. I was totally off guard," he said.