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The operator of an earthquake-ravaged nuclear plant said Wednesday a radioactive leak from the plant was 50 percent bigger than first reported two days ago. The mayor ordered the facility closed until its safety could be confirmed.

Tokyo Electric Power Co. also said about 400 barrels containing low-level radioactive waste at the Kashiwazaki-Kariwa nuclear plant were knocked over, and the lids had come off 40 of them, as a result of Monday's deadly 6.8-magnitude quake. The announcement revised the company's earlier estimate of 100 tipped barrels.

"We made a mistake in calculating the amount that leaked into the ocean. We apologize and make correction," Tokyo Electric said in a statement. Spokesman Jun Oshima said the amount of radioactive water that leaked into the Sea of Japan was still "one-billionth of Japan's legal limit."

Tokyo Electric spokesman Tsutomu Uehara said no radiation has been detected outside the nuclear plant.

Japanese automakers, meanwhile, called production halts Wednesday at factories because of quake damage at a major parts supplier. Production was scaled back at Toyota Motor Corp., Nissan Motor Co. Mitsubishi Motors Corp. and Fuji Heavy Industries.

Toyota, Japan's No. 1 automaker, will stop production lines at a dozen factories centered in central Aichi prefecture Thursday afternoon and Friday. The shutdown was due to the temporary closure of Riken Corp.'s plant at Kashiwazaki, near the epicenter of Monday's quake.

Toyota will assess the situation at Riken, supplier of key transmission and engine parts, before deciding whether to resume production Monday, he said.

Repair workers on Wednesday climbed over the Kashiwazaki-Kariwa's three-story transformer building, which was charred from top to bottom in a fire Monday.

A tour given to Japan's Communist Party chief, Kazuo Shii, and reporters revealed widespread damage across the sprawling compound, including large cracks in roads, toppled concrete fences and buckled sidewalks.

"This is unforgivable," Shii told TEPCO Deputy Superintendent Masakazu Minamidate. "You say there's no leak before you really know. ... The delay in information was especially inexcusable."

TEPCO President Tsunehisa Katsumata toured the site earlier, declaring it "a mess" and apologizing for "all the worry and trouble we have caused."

"We will conduct an investigation from the ground up. But I think fundamentally we have confirmed that our safety measures worked," he said.

Hiroshi Aida, mayor of Kashiwazaki, a city near the epicenter that is home to the plant and 93,500 people, ordered operations at the plant halted Wednesday for "safety reasons."

The malfunctions and a delay in reporting them fueled concerns about the safety of Japan's 55 nuclear reactors, which have suffered a string of accidents and cover-ups. Nuclear power plants around Japan were ordered to conduct inspections.

Adding to the urgency of any investigation was new data from quake aftershocks that suggested a fault line may run underneath the mammoth power plant.

The Kashiwazaki-Kariwa plant, located 135 miles northwest of Tokyo, has been plagued with mishaps. In 2001, a radioactive leak was found in the turbine room of one reactor. It is the world's largest nuclear plant in power output capacity. '

Signs of problems after the quake Monday came first not from the officials, but in a plume of smoke after the quake triggered a small fire at an electrical transformer. Twelve hours later, the company announced the quake also caused a leak of about 315 gallons of water containing radioactive material.

Later Tuesday, it said 50 cases of "malfunctioning and trouble" had been found. Four of the plant's seven reactors were running at the time of the quake, and they were all shut down automatically by a safety mechanism.

Meanwhile, TEPCO spokesman Hiroshi Itagaki said that information accumulated by studying aftershocks shows that a fault line stretches under the ocean near the coast, which is not far from the plant. He declined to say how close to the plant the fault might come.

Osamu Kamigaichi, an official at Japan's Meteorological Agency, which monitors earthquakes, said it was possible the fault line stretched to underneath the plant grounds.

Across the town, more than 8,000 residents hunkered down for their second night in shelters. Late Wednesday, police discovered a 76-year-old man crushed to death under a temple in Kashiwazaki, bringing the quake's fatalities to 10.

For residents, thousands of whom work at the plant, the controversy over its safety compounded already severe problems, which included heavy rains and the threat of landslides, water and power outages.

"Whenever there is an earthquake, the first thing we worry about is the nuclear plant. I worry about whether there will be a fire or something," said Kiyokazu Tsunajima, a tailor who sat outside with his family, afraid an aftershock might collapse his damaged house.

The area around Kashiwazaki was hit by an earthquake three years ago that killed 67 people, but the plant suffered no damage.

The plant's safety record and its proximity to a fault line prompted residents to file lawsuits claiming the government had failed to conduct sufficient safety reviews when it approved construction of the plant in the 1970s. But in 2005, a Tokyo court threw out a lawsuit filed by 33 residents, saying there was no error in the government safety reviews.

Monitor the situation in FOXNews.com's Natural Disasters Center.