TOKYO (AFP) - Health complications stemming from Japan's 2011 tsunami have killed more people in one Japanese region than the disaster itself, the local authority said Thursday.

Data compiled by officials and police show that almost three years after the huge waves smashed ashore, 1,656 people living in Fukushima prefecture have died from stress and other illnesses related to the disaster, compared with 1,607 who were killed in the initial calamity.

"The biggest problem is the fact that people have been living in temporary conditions for so long," said Hiroyuki Harada, a Fukushima official dealing with victim assistance.

"People have gone through dramatic changes of their environment. As a result, people who would not have died are dying," he said.

Along with the prefectures of Miyagi and Iwate, Fukushima was one of the worst hit parts of Japan when a huge 9.0 undersea earthquake sent a wall of water barrelling into the coast.

The waves swept more than 18,000 people to their deaths across the country, and destroyed entire communities.

Fukushima was also hit with the resulting nuclear disaster after cooling systems at the Daiichi nuclear plant were knocked out, sending reactors into meltdown and forcing the evacuation of tens of thousands of people.

Almost three years on, many people remain displaced, whether because their homes around the power plant have not been declared safe or because rebuilding along the coast has been slow.

Officials say that as well as those who died in the early stages of the disaster, through lack of initial care because medical facilities were hobbled, a growing number of people are dying from the physical and mental stress of staying at shelters, including through suicide.

"This is different from normal, natural disasters. People who live in shelters are forced to live there, away from their home towns and villages, where they lived for a long time," Harada said.

"They are forced to live the kinds of lives they are not used to." According to the Reconstruction Agency, up until September around 90 per cent of those dying from indirect causes were 66 or older, Kyodo News reported.

While both Iwate and Miyagi suffered higher tolls in the initial disaster, the number of indirect deaths in both prefectures is lower than in Fukushima, at 434 and 879 respectively.

The small Fukushima city of Minamisoma has been the worst-hit, with 447 deaths indirectly blamed on the disaster, followed by 317 in Namie town and 225 in Tomioka town.

Parts of Minamisoma and all of Namie and Tomioka remain off-limits because of still-elevated radiation levels.