A GREENS policy to improve the health of Australia's youth calls for a ban on junk food advertising during children's television hours.

Under the proposal, announced on Thursday, junk food advertising would be banned on commercial TV between 6-9am and 4-9pm on weekdays, from 6am-noon and 4-9pm on weekends and during school holidays, and children's pay television channels would be prevented from screening junk food ads at any time.

Further, companies using emails and smartphones to target underage customers would be banned from sending material promoting unhealthy foods.

Greens' health spokesman Dr Richard Di Natale said there was a looming health crisis in Australia.

"The relentless marketing of junk food to children is contributing to a childhood obesity crisis in this country that will cause diabetes and heart disease to skyrocket in the coming decades," Senator Di Natale said.

"Something must be done to curb the influence of junk food promotion on our kids and unfortunately self-regulation in Australia has clearly failed."