The Defense Ministry said about 20,000 Self-Defense Forces troops, 190 aircraft and 25 vessels had been dispatched Saturday to the area around Sendai, where tsunami waves a day earlier churned whole neighborhoods into debris, crashing through homes and businesses and sweeping trains, trucks and cars into the moving mass of destruction.

Ministry officials were working with the Pentagon on plans to use U.S. naval forces to move 250 rescue vehicles into areas rendered unapproachable by waves that washed away roads and rail lines.

About 69,000 people were stranded at Tokyo Disneyland and Tokyo DisneySea because of road damage and idled mass transit. Theme park workers gave out blankets, heaters and coats to visitors forced to camp outside in 30-degree temperatures.

"Rations and supplies are just starting to reach emergency shelters," said Cabinet Secretary Yukio Edano, dressed in the light-blue jacket that identifies disaster-relief workers.

Images from the coastal city of Soma taken from a TV network helicopter showed trees that had been uprooted by the tsunami and then dragged back to shore when the waters receded.

Video taken over Kesennuma, in Miyagi prefecture, where the quake was most destructive, captured a Self-Defense Forces helicopter swooping low over a neighborhood to pluck a survivor from one of the few rooftops still above water.

In Iwanuma, survivors taking refuge on top of Minamihama Chuo Hospital waved flags and umbrellas to signal for help. All around them were water and the debris of buildings.

At Sendai airport, a small private jet appeared to have been carried by the rushing waters and left partly buried in waterlogged rubble. Most of the runway was under water.

Crews labored through the night to dig out trucks and cars that had fallen into chasms in roads and highways. At a Machida district shopping center in Tokyo, the ramp of a parking lot had collapsed, and workers with cranes were searching for people in the wreckage. One person pried from the rubble was unconscious and in critical condition.

"More than 90% of the houses in three coastal communities have been washed away by tsunami," a municipal official in the town of Futaba told the Kyodo News Agency. He said from his vantage point on the fourth floor of the town hall, "I see no houses standing."

In Fukushima prefecture, a state of emergency was proclaimed after the earthquake knocked out a backup power system, depriving the nuclear reactor facility of the energy needed to cool the fuel rod housing.

Although the temperature in the housing was running 50% above normal, at about 750 degrees Fahrenheit, it remained well below the 2,200-degree limit for preventing "cladding failure," said Margaret Harding, a veteran nuclear industry engineer familiar with the reactor from her work with General Electric.

"Remember, these are ceramic pellets. It takes a lot of heat to melt them," Harding said of the rods.

The Kyodo News Agency said that accumulated vapor from one of the reactors had been successfully released by Saturday afternoon.

Officials of Japan's Nuclear and Industrial Safety Agency insisted that the "slightly radioactive" emissions posed no risk to people or the environment. Radiation levels inside the overheated reactor housing were 1,000 times normal, the agency said, but only eight times normal background at the plant's main gate. Experts explained that the steam carries low-level radiation that rapidly dissipates.

Tens of thousands of people living within a seven-mile radius of the nuclear plant were evacuated as a precaution, Cabinet Secretary Edano told reporters.

Prime Minister Kan visited the stricken nuclear facility in a tour of the disaster areas. He vowed to "make whatever decisions need to be made" as he boarded a helicopter for the aerial tour.

Japan's nuclear facilities have survived many earthquakes. But the Kashiwazaki-Kariwa facility, the world's largest, was forced to close for two years in 2007 after being hit by an earthquake of greater force than the plant was designed to withstand. And Japan has a record of cover-ups when it comes to nuclear accidents. In 2007, the operators of the Shika plant acknowledged they had failed to report a 15-minute uncontrollable nuclear chain reaction eight years earlier. Another operator was forced to close 17 plants temporarily in 2003 after admitting it falsified safety inspection reports.

Japanese Finance Minister Yoshihiko Noda said the government would tap a contingency fund to cope with the massive damage, according to Kyodo New Agency.

Japan is already facing some of the highest public debt of any industrialized nation, running at about 200% of its annual economic output.

"To be honest I'm worried about the economy in the short term," said Kazu Hoshiai, 43, a Japan Airlines worker. "We are accustomed to earthquakes but not like this one."

Photos: Scenes from the earthquake

Magnier and Demick reported from Tokyo and Williams from Los Angeles. Special correspondent Kenji Hall in Tokyo and Times staff writers Bruce Wallace and Brady MacDonald in Los Angeles and David Pierson in Beijing contributed to this report. Benjamin Haas in the Times' Beijing bureau also contributed to this report.