Oncologists across the country are backing a campaign to raise the age anyone can buy cigarettes from 18 to 21.

Cancer specialists across the country want to make it illegal for anyone below the age of 21 to purchase cigarettes.

The Medical Oncology Group of Australia and the Private Cancer Physicians of Australia want the legal age in Australia raised from the current 18.

"We know from research that 95 per cent of all adults start smoking before they turn 21, said MOGA chair Chris Karapetis.

"We also know if you can prevent young people from taking up the deadly habit by the time they turn 21, the chances of them ever smoking at all is very low".

Christopher Steer, head of the Private Cancer Physicians of Australia, says smoking rates among disadvantaged youth is alarmingly high, and significantly higher in regional Australia than in the cities.

According to government figures, 15,000 Australians die from smoking-related illnesses every year.

"Smoking is the most preventable cause of cancer in Australia," said Dr Karapetis.