Japanese rescuers dug through the rubble of collapsed buildings and mud on Saturday to reach people trapped after a powerful 7.3 magnitude earthquake struck a southern island, killing at least 25 people and injuring more than a thousand.
The shallow earthquake hit in the early hours of Saturday, sending people fleeing from their beds and onto dark streets, and follows a 6.4 magnitude quake on Thursday which killed nine people in the area.
"I felt strong shaking at first, then I was thrown about like I was in a washing machine," said a Tokai University student who remains isolated in the village of Minamiaso in Kumamoto province on the island of Kyushu.
"All the lights went out and I heard a loud noise. A lot of gas is leaking and while there hasn't been a fire, that remains a concern," the student, who is sheltering in a university gym with 1,000 other students and residents, told Japanese media.
Prime Minister Shinzo Abe said the speed of rescue efforts was critical given that wet weather is forecast overnight, which could further damage weakened buildings and cause landslides.
"Nothing is more important than human life and it's a race against time. I want rescue activities to continue with the utmost effort," Abe said at a government meeting after the disaster.
The epicentre of the quake was near the city of Kumamoto and measured at a shallow depth of 10 kms (6 miles), the USGS said.
Television footage showed fires, power outages, collapsed bridges and gaping holes in the earth. Residents near a dam were told to leave because of fears it might crumble, broadcaster NHK said.
The city's 400-year-old Kumamoto Castle was badly damaged, with its walls breached after having withstood bombardment and fire in its four centuries of existence.
The quake triggered a tsunami advisory which was later lifted and no irregularities were reported at three nuclear power plants in the area, a senior government official said.
Bank of Japan Governor Haruhiko Kuroda, speaking at a G20 event in Washington, said it was too early to assess the economic impact but bank operations in Kumamoto were normal.
Electronics giant Sony Corp. said a factory producing image sensors for smartphone makers will remain closed while it assesses the damage from the quakes. One of its major customers is Apple which uses the sensors in iPhones.
Toyota Motor Corp. halted production at three plants producing vehicles, engines and trans axles in Fukuoka. Toyota said there was no damage at its plants, but it was checking the status of its suppliers. It will decide on Sunday whether to resume production.
Nissan Motor Co. Ltd. stopped production at its Fukuoka plant which produces vehicles including the Serena, Teana, Murano and Note.
Many frightened people
Chief Cabinet Secretary Yoshihide Suga said nearly 80 people were believed trapped or buried in rubble. Rescuers managed to pull 10 students out of a collapsed university apartment in the town of Minami on Saturday.
Extra troops would be sent to help, with up to 20,000 due by Sunday, as well as more police, firefighters and medics, he said. "We are making every effort to respond," Suga said.
Many frightened people wrapped in blankets sat outside their homes while others camped out in rice fields in rural areas surrounding the main towns.
About 170,000 households were without power and 385,000 without water, Suga said.
"I don't mind standing in line. I'm just thankful for some food," said a man in his 60s waiting in line for meals served by Self Defense Forces personnel in the town of Mashiki, close to the epicentre.
The region's transport network suffered considerable damage with one tunnel caved in, a highway bridge damaged, roads blocked by landslips and train services halted, Japanese media reported. Kumamoto airport was also closed.
There have been more than 230 aftershocks of at least level 1 on the Japanese scale since Thursday's shock, said Japan's meteorological agency.
"We have already seen of several of the mid to upper 5 plus magnitude range, and over the next several days and weeks, we would not be surprised to see more earthquakes of this size," said John Bellini, a geophysicist with the U.S. Geological Survey (USGS).
Japan is on the seismically active "ring of fire" around the Pacific Ocean and has building codes aimed at helping structures withstand earthquakes.
A magnitude 9 quake in March 2011 north of Tokyo touched off a massive tsunami and nuclear meltdowns at Fukushima. Nearly 20,000 people were killed in the tsunami
The 2011 quake temporarily crippled part of Japan's auto supply chain in particular, but some companies have since adjusted the industry's "Just in Time" production philosophy in a bid to limit any repeat of the disruption.