KASHIWAZAKI, Japan — A strong earthquake shook Japan’s northwest coast yesterday, setting off a fire at the world’s most powerful nuclear-power plant and causing a reactor to spill radioactive water into the sea — an accident not reported to the public for hours.
The magnitude-6.8 temblor killed at least eight persons and injured more than 900 as it toppled hundreds of wooden homes and tore 3-foot-wide fissures in the ground. Highways and bridges buckled, leaving officials struggling to get emergency supplies into the region.
About 10,000 people fled to evacuation centers as aftershocks rattled the area. Tens of thousands of homes were left without water or power.
The quake triggered a fire in an electrical transformer and also caused a leak of radioactive water at the Kashiwazaki Kariwa nuclear-power plant, the world’s largest in terms of electricity output.
The leak, announced many hours after the quake, fed fresh concerns about the safety of Japan’s 55 nuclear reactors, which supply 30 percent of the quake-prone country’s electricity and have suffered from a long string of accidents and cover-ups.
About 315 gallons of water apparently spilled from a tank at one of the plant’s seven reactors and entered a pipe that flushed the water into the sea, said Jun Oshima, an executive at Tokyo Electric Power Co.
Officials said there was no “significant change” in the seawater near the plant, which is about 160 miles northwest of Tokyo. “The radioactivity is one-billionth of the legal limit,” Mr. Oshima said of the leaked water.
Eliot Brenner, a spokesman for the U.S. Nuclear Regulatory Commission in Washington, said the agency told Japan’s government it was ready to provide assistance if needed but had not received any request for help.
In Kashiwazaki, the hardest-hit city, the quake reduced older buildings to piles of lumber. Eight persons in their 70s and 80s — five women and three men — died, most of them crushed by collapsing buildings, the National Police Agency said.
The Kyodo News agency reported more than 900 people were hurt, with injuries including broken bones, cuts and bruises.
“I got so dizzy that I could barely stand up,” said Kazuaki Kitagami, a worker at a 7-Eleven convenience store in Kashiwazaki. “The jolt came violently from just below the ground.”
The area was plagued by aftershocks, but there were no immediate reports of additional damage or casualties. Near midnight, a magnitude-6.6 quake hit off the west coast, shaking wide areas of Japan, but it was unrelated to the Niigata quake to the north, and there were no immediate reports of damage.
Japan sits atop four tectonic plates and is one of the world’s most earthquake-prone countries.
In October 2004, a magnitude-6.8 earthquake hit Niigata, killing 40 persons and damaging more than 6,000 homes. It was the deadliest to hit Japan since 1995, when a magnitude-7.2 quake killed 6,433 persons in the western city of Kobe.
The last major quake to hit Tokyo killed about 142,000 people in 1923, and specialists say the capital has a 90 percent chance of suffering a major quake in the next 50 years.
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