A controversial 20 per cent sugary drink tax has been proposed by the Greens, drawing support from doctors but has been rejected by the government.

The Greens want to impose a 20 per cent tax on soft drinks and fruit juices in a bid to address growing childhood obesity.

The proposal has been welcomed by doctors but rejected outright by the Turnbull government.

Greens leader Richard Di Natale says with one in three children classified as obese, life expectancy for the next generation will go backwards.

"We know from the evidence overseas that if we put a small tax on sugary sweetened drinks, a major contributor to obesity and ischemic heart disease, we will reduce the incidence of both of these things," he told ABC radio on Wednesday.

Sugary drink taxes have been introduced in several countries including the United Kingdom and France.

Academic research quoted by the Greens shows a 20 per cent sugary drink tax would save 1600 lives and the health system up to $609 million over twenty years.

A recent study found 30 per cent of added sugar consumed by Australians comes from sugary drinks, and modelling suggests a tax would reduce this by 12 per cent.

Doctors have welcomed the proposal as a step in the right direction and are cautiously supportive of the idea.

Australian Medical Association president Michael Gannon said sugary drinks are part of the growing obesity problem, which is the number one health epidemic facing the country.

Dr Gannon stressed any changes shouldn't demonise sugary drinks in general or target specific fast-food outlets.

The World Health Organisation has recommended sugary drink taxes and celebrity chef Jamie Oliver has campaigned for Australia to introduce the measure.

Finance Minister Mathias Cormann rejected the concept outright.

"There are actually some things that are the responsibility of individual Australians, parents and families," he told reporters in Canberra.

He said every issue should not be addressed by a new tax.

Labor frontbencher Katy Gallagher said a range of interventions was needed to tackle the scourge of childhood obesity such as nutrition education, promoting physical activities and preventative health programs.

A sugar tax was not Labor policy at this point, she told reporters.

Coalition senator Barry O'Sullivan savaged the Green's tax policy, saying the party had failed to address other public health dangers.

"The Greens must explain why they have chosen not to address toxic lawn mower fumes, which have potentially reached epidemic levels across suburban Australia."