Temperatures have begun to sink toward freezing in northeastern Japan, compounding the misery for survivors coping without water, electricity or proper food in the region battered by Friday's tsunami.
Japan's prime minister says the country is facing its most severe challenge since World War II.
Officials say at least 1,400 people were killed.
But the police chief of Miyagi state says the death toll there alone could pass 10,000.
Japanese troops today rescued a survivor about 10 miles offshore.
The tsunami had swept the 60-year-old man out to sea as he clung to the roof of his home.
The man told his rescuers that he and his wife were trying to gather their belongings when the tsunami hit.
She was swept away.
Meanwhile, Tokyo Electric Power says it will ration electricity with rolling blackouts in parts of Tokyo and other cities.
The planned blackouts of about three hours each will start tomorrow.
They are meant to help make up for a severe shortfall after key nuclear plants were left inoperable due to the earthquake and tsunami in northeastern Japan.