As the mercury plunges in Japan's disaster-hit northeast, thousands of people in temporary homes are digging in for what could be a long, hard and very cold winter.

Swirling snow and driving winds will add to the misery of tsunami survivors in a region where the temperature frequently dips below freezing through December, January and February.

Many lost their homes when the monster waves of March 11 swept ashore, killing 20,000 people and grinding whole neighbourhoods into matchwood.

In Ishinomaki, one of the hardest-hit coastal settlements, more than half of the city's 61,000 houses were either swept away completely or severely damaged by the towering tsunami.

City authorities have built more than 7,000 temporary homes that are now providing shelter for around 6,800 families.

Heaters, insulation, new tatami straw mats and even electrically heated toilet seats have all been provided, a city official told AFP.

A further 6,500 families have moved into apartments rented by the local government on their behalf.

But thousands of others are not so fortunate.

Ishinomaki officials concede they are unsure how up to 20,000 families will be keeping warm this winter.

"They must be either staying with relatives far away or living in their own house if the damage was not so bad," an official told AFP.

"But we don't have much information about them."

Hideko Kamiyama and her family were confined to the upper floor of their partially-destroyed home for months, as they patiently waited for craftsmen to transform the downstairs from a fetid mess of broken and rotting timbers.

"Our house was almost completely destroyed in the disaster, but many volunteers and carpenters worked hard to repair it," she said, wrapping her jacket tighter against the cold.

"It's 80 percent repaired now, and volunteers gave us heaters and carpets.

"(They also) gave me various things such as patches you can stick on your back to warm you up. I think I can handle the winter now, no matter how cold it gets," Kamiyama said.

In a town that registered a low of minus eight degrees Celsius (17 degrees Fahrenheit) in February, Kamiyama will need all the warmth she can get.

But she is not going to find it from her neighbours.

"There was a house here before," she said pointing to a vacant lot next to her own which was torn down after suffering irreparable damage when the waves hit.

People allocated temporary homes have few complaints about the austere conditions in which they live, but are desperately hoping a more permanent solution can soon be found.

Ishio Abe and his family of five have been living in just three rooms since May.

The homes are intended to be used for just two years, but, says Abe, he does not know if this will be long enough.

"We were given a stove as well as electric carpets. I think we are good for now but I have no job and I wonder what I am going to do next," he said.

Yoshinori Sato of the Ishinomaki city council said authorities are working hard, but they know that real recovery will only come when residents have a sense of long term security.

"Rebuilding houses takes time, we dont really know how long yet," he said.

"Once we have some idea, we can start telling the people when they can move back into real houses."