The proposed changes to increase the age from 18 would save the state $220 million in largely health-related costs over the next decade, Mr Xenophon says.

"This will save lives and precious dollars, which could be used elsewhere. The time has come for this to happen and many people will be asking why it didn't happen sooner," he said.

Australia's peak oncology group has backed the move, pointing to evidence that shows the number of people who start smoking over the age of 21 is low.

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

"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."

Health Minister Peter Malinauskas said his party was willing to look at any "evidence-based" measures to decrease the uptake of smoking.

"We have stated we are willing to contemplate any legislative reform that will see a reduction in smoking," Mr Malinauskas told ABC Radio.

The Liberal opposition is also willing to look at the policy but health spokesman Stephen Wade said the reasons for people taking up smoking were complex.

"It is very important to remember the legal age to buy cigarettes is only one of the factors," Mr Wade said.