While the disease was previously ranked seventh, this year's Australian Bureau of Statistics (ABS) research show that deaths from dementia have more than doubled in the past decade.

Heart disease, stroke and lung cancer are the top three diseases.

In NSW, 74,000 people have dementia, with 227,000 expected to be directly affected by 2050.

A recent report by Access Economics for Alzheimer's Australia predicted an increase in the number of people who have dementia from 230,000 in 2008 to 465,000 in 2030, and to more than 730,000 in 2050.

In 2005, a report also found that western and south-western Sydney had the lowest rates of dementia as a proportion of the population, but were expected to see the largest increase in dementia until 2050.

Western Sydney was expected to have a fourfold increase in dementia.

Alzheimer's Australia NSW chief executive John Watkins said the numbers were startling, demonstrating the growing momentum of the condition.

``The ABS statistics highlight the critical need for immediate action into planning for the significant health, social and economic impacts on Australian society these dementia figures represent,'' he said.

``Now is the time to take a long-term view and plan for the future of aged care and dementia-care services in Australia.

``An increase in funding for medical research is now also urgently needed to ensure adequate prevention measures and even a cure for dementia.''