Rich and poor countries alike must invest more in mental health care, especially during economic crises when rates of depression and suicide tend to rise, the World Health Organization (WHO) said on Tuesday.

One in 10 people worldwide has a mental health disorder but only one percent of the global health workforce is treating such illnesses, which are still widely stigmatised, the United Nations agency said.

"The resources devoted to mental health, financial as well as human resources, remain extremely small all over the world," Dr. Shekhar Saxena, Director of WHO's Department of Mental Health and Substance Abuse, told a news briefing.

In countries caught up in war or natural disasters, demands on mental health services increases but budgets shrink, he said.

"In general, countries that are facing serious socio-economic challenges are at a higher risk of having mental health problems within their communities," Saxena said.

"The rate of depression and the rate of suicide actually do increase significantly for countries that are suffering from economic downturn. These are precious loss of life which a country should protect by maintaining the mental health care that is due to these people during these times of stress."

There is also huge inequality in mental health care.

Nearly half of the world's population lives in a country where there is less than one psychiatrist per 100,000 people, while in high-income countries the rate is one per 2,000, according to WHO's 2014 Mental Health Atlas issued on Tuesday.

"Many [rich] countries are devoting enough resources but the utilization of those resources is not optimum. Too many efforts are being made for people who are in-patients in mental hospitals and otherwise in custodial care and too few resources are spent on community care," Saxena said.

For severe disorders such as schizophrenia and bipolar disorder, prevalence rates are similar worldwide, he said.

"The prevalence of depression, anxiety, post-traumatic stress disorders and drug abuse vary significantly more between different societies and there are some cultural factors for that," he said.