Japan should use a higher rate of mental health problems after the Fukushima nuclear accident to update outdated attitudes to depression in the country, a top health official said Monday.

Speaking at the World Health Summit in Berlin, Shekhar Saxena, from the mental health division of the World Health Organisation, said the mental aspects of disasters tended to be ignored in the aftermath of a natural disaster.

"Mental health treatment is needed for almost everyone who is affected by the disaster," Saxena told a packed audience at the summit. "Unfortunately, some neglect occurred."

Officials have previously warned of an increase in depression cases in a country where this illness still carries a stigma largely overcome in the West.

It is only recently that urban areas of Japan have begun to tackle the taboo surrounding depression, a condition euphemistically known as "heart 'flu" in the country.

After a disaster such as the Fukushima accident, the prevalence of severe mental disorders, such as psychosis, increase from two to three percent of the population to three to four percent, said Saxena.

More mild mental disorders like depression increase from one in ten people to one in five, he added.

Treating such disorders is best done within the community rather than in medical institutions, he said, arguing for an overhaul of attitudes and the system in Japan.

"In Japan, mental health care is largely undertaken by specialised institutions whereas it is more effective if it is undertaken at a community level," he said.

"We recommend for Japan to utilise the opportunity presented by the disaster to actually change the system to make it more community-oriented."

Shunichi Fukuhara, from the Kyoto University School of Medicine and Public Health, told AFP that Japanese people were tending to bottle up their feelings about the tragedy, making treating them harder.

"It's a real issue in Japan, and throughout Asia, especially among men ... Maybe it's the Samurai spirit. People don't like to admit they are depressed."

Another expert, Shunichi Yamashita, from Fukushima medical university, said the tragic war-time history of the Japanese had sparked greater anxiety than might have been the case elsewhere in the world.

"People in Japan are very much aware of the risks from radiation from the atomic bombs in Hiroshima and Nagasaki, so they worry more," said Yamashita.

Yamashita, who moved from Nagasaki to Fukushima to assist in the response to the accident, said Japan needed an "unprecedented effort" to monitor the health impact of the disaster.

He is currently working on a survey of two million people.

"There are uncertainties about the risks of chronic low-dose radiation exposures for human health but there is no alternative than to take the responsibility of monitoring the health condition of people around Fukushima."

The March 11 earthquake triggered a tsunami that tore into Japan's northeast coast, leaving 20,000 people dead or missing and sparking meltdowns and explosions at the Fukushima Daiichi nuclear power plant.

It was the world's worst nuclear disaster since the Chernobyl meltdown and prompted a raft of health fears, both physical and mental.