More than 12,000 people huddled in evacuation centres in northwest Japan on Tuesday after an earthquake flattened homes, killing nine elderly people, injuring around 1,000 and triggering a leak of contaminated water from a nuclear plant.
As aftershocks continued, forecasts for wet weather raised fears of mudslides that could add to the devastation.
"I am worried about the aftershocks," said 80-year-old Toshiko Kojima, who said she had spent a mostly sleepless night in a crowded elementary school gymnasium in the worst-hit city of Kashiwazaki, too afraid to go home.
A small fire and a leak of contaminated water at Tokyo Electric Power Co's (TEPCO) Kashiwazaki-Kariwa nuclear power plant -- the world's largest -- reignited fears about nuclear safety in a country that relies on atomic power for about one third of its electricity.
Water, gas and electricity supplies were cut by the 6.8 magnitude quake that hit Niigata prefecture at 10:13 am (0113 GMT) on Monday, which also caused a small radiation leak and fire at the world's biggest nuclear plant.
With more than 300 homes totally destroyed in Kashiwazaki alone, it was unclear when people could go home and worries were mounting about the health of evacuees, many of whom are elderly.
"The damage was worse than anticipated," Mayor Hiroshi Kaeda told reporters. "If we can restore water service, more people can go home to live, so that is what we want to do first."
In Kashiwazaki, people lined up with plastic bottles for fresh water, which was trucked in by local officials and a contingent of about 500 members of the armed forces.
The navy shipped in emergency rations, convenience stores and supermarkets gave out rice balls and bottled water, and smiling soldiers in camouflage uniforms and helmets made rice balls and distributed them at schools and other evacuation centres.
The quake halted gas service to about 35,000 homes and disrupted the water supply to all of Kashiwazaki, a city with a population of around 95,000 whose economy relies on nuclear power generation and fishing. More than 25,000 homes and other places.
TEPCO said water containing radioactive materials had leaked from a unit at its Kashiwazaki-Kariwa nuclear power plant. The contaminated water was also released into the ocean, but had had no effect on the environment.
The quake was stronger than those its reactors had been designed to withstand, the company added.
A fire in an electrical transformer at the plant was quickly extinguished but it was unclear when TEPCO could restart three power units there.
Media as well as local residents urged the nuclear power industry to take heed of the threat.
"Nuclear power companies must not only keep in mind the quake resistance of buildings and facilities, but must take full precautions so that people in the vicinity and all citizens will trust that if there is a quake, nuclear reactors will be safe," the Nikkei newspaper said.
Retired taxi driver Tomiji Okura, 72, said the nuclear industry had boosted his business, but reactors had to be able to withstand earthquakes. "When you have something like this, it's scary. I want them to be made safe," he said.
Prime Minister Shinzo Abe cut short campaigning for the July 29 parliamentary elections to inspect damage on Monday.
It was unclear when production would re-start at some factories in the area, including a Fuji Xerox printer factory.
Japan is one of the world's most earthquake-prone countries, with a tremor occurring at least every five minutes.
Houses, many wooden with traditional heavy tile roofs, collapsed and roads cracked in Monday's quake, centred in the same northwestern area as a tremor three years ago.
Niigata was hit in October 2004 by a quake with a matching magnitude of 6.8 that killed 65 people and injured more than 3,000. It was the deadliest quake in Japan since a magnitude 7.3 tremor hit Kobe city in 1995, killing more than 6,400.
"My house is still standing, but inside it's a complete mess. The tiles have fallen off the walls," said Shigeru Yokota, 27, an electrical repair worker.
"This happened three years ago as well. It is rubbing salt in the wound."