A 20 per cent tax on sugary drinks is being proposed by Australia's leading health organisations as part of a tough new strategy to tackle obesity, which they now say poses a greater risk to the nation than smoking.

A coalition of 34 high-profile groups including the Obesity Policy Coalition, Cancer Council, Royal Children's Hospital Melbourne and the Stroke Foundation are calling on the federal government to establish obesity prevention as a national priority.

The strategy includes a ban on unhealthy food advertising on free-to-air television during prime time, between 5.30pm and 9.30pm, when they say the greatest numbers of children are watching.

"This is really urgent," said Obesity Policy Coalition executive manager Jane Martin.

"We have a generation of children that could die younger than their parents."

Rates of obesity continue to climb in Australia, with about 63 per cent of adults and 27 per cent of children obese or overweight.

The action plan, titled "Tipping the Scales" and launched on Tuesday, renews calls for a tax on sugary drinks, with a suggested levy of 20 per cent.

The levy could apply to all non-alcohol drinks with added sugar such as soft drinks, energy drinks, sports drinks and cordials, but exclude 100 per cent fruit juices and milks.

Applying a tax on sugary drinks would follow in the footsteps of Britain, Ireland, Belgium, France, Fiji, Mexico, South Africa and regions in the United States, where sugar taxes have or are about to be applied.

In Mexico, it has been reported a tax of about 10 per cent on sugar-sweetened beverages saw a 7.6 per cent drop in purchases of those drinks over two years. This is disputed by the beverage industry.

The action plan also calls for Australia's Health Star Rating System, which rates packaged foods out of five stars, to be made mandatory by July 2019. It is hoped the change will encourage more food manufacturers to improve the nutritional value of their products.

Other suggested policies include developing a national active travel strategy, funding new education campaigns around diet and exercise, and establishing a national taskforce on obesity.

Anna Peeters, Professor of Epidemiology and Equity in Public Health at Deakin University, said foods and drinks that should be consumed only occasionally had become part of people's regular diet.

In 1980 only about 1 in 10 Australians were obese, she said.

"Now it is much closer to a third."

Health Minister Greg Hunt is unlikely to support a new tax.

A spokesman for the minister said "as the minister has said on many occasions before, the government does not support a new tax on sugar to address this issue".

"We don't believe increasing the family grocery bill at the supermarket is the answer to this challenge.

"Obesity and poor diets are complex public health issue with multiple contributing factors, requiring a community-wide approach as well as behaviour change by individuals."

The coalition of lobby groups for Australian food and beverage manufacturers and producers broadly supported the action plan, though there was concern that industry had been excluded from its development.

They said that significant improvements had been made when public health groups partnered with industry, pointing to the rapid uptake of voluntary health star ratings system, which is currently under review.

A spokesman from the Australian Beverages Council said "our members have overwhelmingly chosen to voluntarily adopt the scheme and display the [health star rating] icon on their products". But the council argued that soft drink taxes elsewhere had not resulted in reduced consumption.

Melbourne woman Andrea Casey, 53, hopes that mandatory health star rating on all packaged foods might help her flex her willpower, while trying to say no to potato chips and chocolate.

Mrs Casey said she has been motivated to lose weight since she was diagnosed and treated with breast cancer in 2012, however finds it hard to resist the snacks her husband buys.

"I eat healthy all day when I'm at work," she said. "But my husband will sit next to me at night with a great big bag of chips and block of chocolate."

"Chips are my thing. I can resist until I have one."