Almost two in three Australians are now overweight or obese, with Australians living outside major cities the most likely to have a body mass index (BMI) beyond the healthy range.

Australia is the fifth most overweight and obese among all OECD countries, with 11.2 million adults (63 per cent) and 1.2 million children (26 per cent) with a BMI 25 or higher.

Sydneysiders were among those least likely to be overweight or obese, according to the latest report from the Australian Institute of Health and Welfare (AIHW).

Northern Sydney had the lowest rate of overweight or obese adults in Australia (53 per cent), with Central and Eastern Sydney (57 per cent) and South-western Sydney (58 per cent) having the third and fourth lowest rates respectively.