Army troops and other rescuers rushed to save scores of trapped residents after two strong earthquakes in south-western Japan killed at least 41 people, injured about 1,500 and left hundreds of thousands without electricity or water.
Rain was forecast to start pounding the area overnight, threatening to further complicate the relief operation and set off more mudslides in isolated rural towns, where people were waiting to be rescued from collapsed homes.
Police said 32 people died in the magnitude-7.3 quake and aftershocks that shook the Kumamoto region on the south-western island of Kyushu early on Saturday. Nine died in a magnitude-6.5 quake that hit the same area on Thursday night.
Four people were missing in Minamiaso. The village near Mount Aso volcano appears to have been the hardest hit by the second earthquake.
Nearly 200,000 homes were without electricity, and drinking water systems also failed in the area.
TV video showed people huddled in blankets, sitting or lying down shoulder-to-shoulder on the floors of evacuation centres. An estimated 400,000 households were without running water.
Hundreds of people lined up for rations at shelters before nightfall, bracing for the rain and strong winds that were expected. Local stores quickly ran out of stock and shuttered their doors, and people said they were worried about running out of food.
"I could hear the noise of all my dishes come crashing down, the rattling, and I was shocked and sad, now I've lost all my dishes," said Ayuko Sakamoto, who was among those in line for the food.
Chief Cabinet Secretary Yoshihide Suga said 1,500 people were injured in the quakes. And Kumamoto prefectural official Riho Tajima said 184 people were injured seriously, and more than 91,000 people were evacuated from their homes.
More than 200 homes and other buildings were either destroyed or damaged, she said.
Prime Minister Shinzo Abe expressed concern about secondary disasters as forecasters predicted rain and strong winds later in the day. With the soil already loosened by the quakes, rainfall can set off mudslides.
"Daytime today is the big test" for rescue efforts, said Mr Abe. Landslides have already cut off roads and destroyed bridges, slowing down rescuers.
Police received reports of 97 cases of people trapped or buried under collapsed buildings, while 10 people were caught in landslides in three municipalities in the prefecture.
TV video showed a collapsed student dormitory at Aso city's Tokai University that was originally two floors, but now looked like a single-story building. A witness said he heard a cry for help from the rubble. Two students were reported to have died there.
In the town of Mashiki, where people were trapped beneath the rubble for hours, an unconscious 93-year-old woman, Yumiko Yamauchi, was dragged out from the debris of her home and taken by ambulance to a hospital.
Her son-in-law Tatsuhiko Sakata said she refused to move to shelter with him after the first quake on Thursday.
"When I came to see her last night, I was asking her: 'Mother? I'm here! Do you remember me? Do you remember my face?' She replied with a huge smile filled with joy. A kind of smile that I would never forget. And that was the last I saw of her," said Sakata.
Among the other casualties were a 69-year-old man who died of head injuries and a 28-year-old woman who suffocated.
The area has been rocked by aftershocks, including the strongest with a magnitude of 5.4 on Saturday morning.
The Japan Meteorological Agency said the magnitude-7.3 quake early today may have been the main one, with the one from Thursday night being a precursor.
David Rothery, professor of planetary geosciences at The Open University in Britain, said the Saturday morning quake was 30 times more powerful than the one on Thursday night.
"It is unusual but not unprecedented for a larger and more damaging earthquake to follow what was taken to be 'the main event,'" he said.
Professor Rothery noted that in March 2011, a magnitude-7.2 earthquake in northern Japan was followed two days later by a magnitude-9.0 quake that caused a devastating tsunami.
"Fortunately, this time the epicentres have been below land rather than under the sea, and no tsunamis have been triggered," he said.
The quakes' epicentres have been relatively shallow - about six miles - and near the surface, resulting in more severe shaking and damage. As many as eight quakes were being felt an hour in the area, it was reported.
One massive landslide tore open a mountainside in Kumamoto's Minamiaso village all the way from the top to a highway below.
Another gnawed at a highway, collapsing a house that fell down a ravine and smashed at the bottom. In another part of the village, houses were left hanging precariously at the edge of a huge hole cut open in the earth.
Mr Suga told reporters that the number of troops in the area was being raised to 20,000, while more police and firefighters were also on the way.
He pleaded with people not to panic, saying: "Please let's help each other and stay calm."
At a hot springs resort, dozens of people trapped were picked up by military helicopters.
Kyushu island's Mount Aso, the largest active volcano in Japan, erupted for the first time in a month, sending smoke rising about 300ft into the air, but no damage was reported.
It was not immediately clear whether there was a link between the quakes and the eruption. The 5,223ft-high mountain is about a 90-minute drive from the epicentre.
The historic Aso Shrine, a picturesque complex near the volcano, was seriously damaged, with a number of buildings with curved tiled roofs flattened on the ground like lopsided fans.
A towering gate, known as the "cherry blossom gate" because of its grandeur, especially during spring, collapsed.
The Nuclear Regulation Authority reported no abnormalities at Kyushu's Sendai nuclear plant.