A road is ripped, flipped and shredded by the quake at Nagaoka. Photo / Reuters

A road is ripped, flipped and shredded by the quake at Nagaoka. Photo / Reuters

More than 12,000 people were spending a second night in evacuation centres in northwest Japan after an earthquake killed nine people, injured more than 1000 and triggered radioactive leaks from a nuclear plant.

A small fire and a leak of 1200 litres of water containing radioactive materials at Tokyo Electric Power Co's Kashiwazaki-Kariwa nuclear power plant - the world's largest - reignited fears about nuclear safety in a country reliant on atomic power for one-third of its electricity.

Hundreds of homes were damaged and water, gas and electricity supplies were cut by the 6.8 magnitude quake that hit Niigata prefecture on Monday.

Nine elderly people were killed and one person was missing, a Niigata prefecture official said. In hard-hit Kashiwazaki City, a team of orange-clad rescue workers with five sniffer dogs said last night that they were calling off operations for the day.

TEPCO had initially said there was no radiation leak, but late on Monday it said water containing radioactive materials had leaked from a unit at its Kashiwazaki-Kariwa nuclear power plant.

Contaminated water reached the sea but had no effect on the environment, the company said, adding that the quake was stronger than its reactors had been designed to withstand.

A fire in an electricity transformer at the plant was quickly extinguished but it was unclear when power units could restart after the trade minister said safety must first be ensured.

Yesterday, the company also admitted that a small amount of radioactive materials - cobalt-60, iodine and chromium-51 - had been emitted into the atmosphere, but that it would take a week or two to figure out the cause.

A Trade Ministry official said the amounts were too small to pose an environmental threat.

Kyodo news agency said about 100 drums containing low-level nuclear waste at the plant were knocked over and some lost their lids, and checks were being made on any environmental impact.

With nearly 800 houses destroyed or damaged in Niigata prefecture alone, it was unclear when people could go home. "I've barely slept," said 35-year-old Kazuko Uchiya, a piano teacher who was at a school-turned-evacuation centre with her 6-year-old son. "I don't know when I can go home. The house is still standing - the structure is okay. But bureaus and shelves have all fallen and I can't get inside. I'm afraid it will shake when I'm inside."