Australians would be prohibited from buying cigarettes until age 21 under a new cancer-fighting plan developed by billionaire mining magnate Andrew Forrest.

Mr Forrest and his wife Nicola are spearheading a major lobbying campaign to convince federal and state governments to raise the legal tobacco purchase age from 18 to 21 – a move they say would stop young people getting hooked, save lives and save government coffers up to $3.1 billion a year.

Mr Forrest and other members of the Eliminate Cancer Initiative – which the Forrests fund through their philanthropic Minderoo Foundation – have already presented the plan to federal Health Minister Greg Hunt and his state counterparts as part of an all-out assault on big tobacco.

The effort comes after Mr Forrest confirmed last week he is considering suing big tobacco companies for the cost of smoking-related illnesses. The plan is based on a landmark Canadian lawsuit in which three companies were ordered to pay more than $15.6 billion in damages.