Two powerful earthquakes a day apart have shaken southwestern Japan, killing at least 29 people and injuring 1500, as thousands of army troops and other rescuers rushed to save scores of trapped residents before the weather turns bad.
The exact number of casualties remained unclear on Saturday.
Rainfall was forecast to start pounding the area, threatening to further complicate the relief operation and set off more mudslides in isolated rural towns, where people were waiting to be rescued in collapsed homes.
Kumamoto Prefectural official Tomoyuki Tanaka said the death toll was climbing, with the latest standing at 19 from Saturday's magnitude-7.3 quake that shook the Kumamoto region on the southwestern island of Kyushu at 1:25am (local time).
On Thursday night, Kyushu was hit by a magnitude-6.5 quake that left 10 dead.
Chief Cabinet Secretary Yoshihide Suga said that 1500 people have been injured, 80 of them seriously.
Nearly 70,000 have left their homes, he said.
Japanese Prime Minister Shinzo Abe expressed concern about secondary disasters as the weather forecast showed rain and strong winds later in the day.
Rainfall can set off mudslides as the soil has already been loosened by the quakes.
"Daytime today is the big test" for rescue efforts, he said.
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, Kyodo News reported.
The area has been rocked by aftershocks, including the strongest with a magnitude of 5.4 on Saturday morning.
The Japan Meteorological Agency said that Saturday's may be the main quake, with the earlier one a precursor.
The quakes' epicentres have been relatively shallow - about 10 kilometres - and close to the surface, resulting in more severe shaking and damage. NHK TV said as many as eight quakes were being felt an hour in the area.
Japanese media reported that nearly 200,000 homes were without electricity. Drinking water systems had also failed in the area. TV footage showed people huddled in blankets, quietly, shoulder to shoulder, on floors of evacuation centres. An estimated 410,000 households are in need of water.
Suga told reporters the number of troops in the area was being raised to 20,000, while additional police and firefighters were also on the way.
He pleaded with people not to panic. "Please let's help each other and stay calm," he said in a televised news conference.
In a hot springs resort, dozens of people trapped were picked up by military helicopters, Asahi TV reported.
Mount Aso, the largest active volcano in Japan which is located on Kyushu, erupted for the first time in a month, sending smoke rising about 100 metres into the air, but no damage was reported. It was not immediately clear if there's a link between the seismic activity and the eruption. The 1592 metre high mountain is about 1 and a half hour's 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, had collapsed, totally damaged. The more than 1700 year-old shrine is designated an "important cultural property" by the government, and has been a popular tourist spot in Kyushu.