More than half of the world's population will be overweight or obese by 2035 without significant action, according to a report.

The World Obesity Federation's 2023 atlas predicts that 51 per cent of the world, or more than four billion people, will be obese or overweight within the next 12 years.

Rates of obesity are rising particularly quickly among children and in lower income countries, the report said.

Describing the data as a "clear warning," Louise Baur, president of the World Obesity Federation, said that policy makers needed to act now to prevent the situation worsening.

"It is particularly worrying to see obesity rates rising fastest among children and adolescents," she said in a statement.

"Governments and policy makers around the world need to do all they can to avoid passing health, social and economic costs on to the younger generation."

The report said childhood obesity could more than double from 2020 levels, to 208 million boys and 175 million girls by 2035.

The cost to society is significant as a result of the health conditions linked to being overweight, the federation said: more than $US4 trillion ($A5.9 trillion) annually by 2035, or 3 per cent of global GDP.

However, the authors said they were not blaming individuals but calling for a focus on the societal, environmental and biological factors involved in the conditions.

The report uses body mass index (BMI) for its assessments, a number calculated by dividing a person's weight in kilograms by their height in metres squared.

In line with the World Health Organisation's guidelines, a BMI score over 25 is overweight and over 30 is obese.

In 2020, 2.6 billion people fell into these categories, or 38 per cent of the world's population.

The report also concluded that almost all of the countries expected to see the greatest increases in obesity in the coming years are low or middle-income countries in Asia and Africa.

The data will be presented to United Nations policy makers and member states next week.