The woman was found inside her home that was washed away, an official said. The woman was conscious but suffering from hypothermia and was being treated at a hospital.
Millions of people have spent four nights with little food, water or heating in near-freezing temperatures as they dealt with the loss of homes and loved ones. Up to 450,000 people are in temporary shelters.
In some parts of Japan Tuesday, fires were not being fought because crews are choosing to ration the water for survivors to drink.
Officials estimate that some 10,000 people who lived in the Miyagi prefecture are now dead. Japan's deadly earthquake is now tied for fourth place on the list for the strongest earthquakes since 1900 after the U.S. Geological Survey upgraded the magnitude to 9.0.
Meantime, at the G8 meeting in Paris, Secretary of State Hillary Clinton met with the Japanese foreign minister to coordinate U.S. relief efforts.
"Today the world comes together to support Japan in its hour of need," said Clinton.
The Associated Press contributed to this report.
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