Meanwhile, nearly 13,000 people packed into evacuation centers such as schools and other secure buildings in the quake zone 160 miles northwest of Tokyo, the Fire and Disaster Management Agency said.

People packed school gymnasiums and community centers in the city, camping out on traditional Japanese futon mattresses and fanning themselves from the muggy summer heat.

Thunderstorms and flooding were expected Tuesday throughout the quake zone, increasing the likelihood that the quake-softened, water-logged ground would give way on hillsides and cause even more damage, officials said.

Light rain began to fall by early afternoon in Kashiwazaki and up to 2.4 inches were expected by Wednesday morning, according to the local observatory.

"The damage is more than we had imagined," Kashiwazaki Mayor Hiroshi Aida said while inspecting damaged areas of his town. "We want to restore the water supply as soon as possible so more people can return home."

Nine people in their 70s or 80s - six women and three men - were killed in the quake, and 19 were seriously injured.

The Defense Ministry dispatched 450 soldiers to the devastated area to clear rumble, search for any survivors under collapsed buildings and provide food, water and toilet facilities. People formed long lines to fill bottles with fresh water.

About 50,000 homes were without water and 35,000 were without gas as of Tuesday morning, local official Mitsugu Abe said. About 27,000 households were without power.

The Japanese Meteorological Agency put the initial quake's magnitude at 6.8, while the U.S. Geological Survey said it was 6.6. The quake, which hit the region at 10:13 a.m., was centered off the coast of Niigata, 160 miles northwest of Tokyo.

The area was plagued by a series of aftershocks, though there were no immediate reports of additional damage or injuries from the aftershocks.

Near midnight, Japan's Meteorological Agency said a 6.6-magnitude 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.

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