The number of people with dementia is expected to almost double to 65.7 million by 2030, according to a World Health Organisationreport published on Wednesday.

By 2050 the number of sufferers could be more than three times the current figure of 35.6 million, the UN body said.

The report published with Alzheimer's Disease International estimates the cost of treating and caring for those with the condition at $604 billion (461 billion euros) a year.

Dementia is caused by a variety of brain illnesses that affect memory, thinking, behaviour and the ability to perform everyday activities.

Alzheimer's disease is the most common cause of dementia and makes up about 70 percent of cases.

The report said far more effective diagnosis was needed, as even in high income countries only 20 to 50 percent of dementia cases are routinely recognised.

"We need to increase our capacity to detect dementia early and to provide the necessary health and social care," said Oleg Chestnov, assistant director general of Noncommunicable Diseases and Mental Health at WHO.

"Much can be done to decrease the burden of dementia. Health-care workers are often not adequately trained to recognise dementia."

Only eight countries worldwide have national programmes in place to address dementia, according to the report "Dementia: a public health priority".

The study also highlights a general lack of information and understanding about the disease, fuelling stigma with the result that people sometimes delay seeking support.

"It is now vital to tackle the poor levels of public awareness and understanding, and to drastically reduce the stigma associated with dementia," said Marc Wortmann, executive director of Alzheimer's Disease International.