Douglas Bettcher of the WHO's Tobacco Free Initiative says governments must take an active role in preventing people from smoking.
He says governments, both rich and poor, need to introduce measures such as aggressive taxation, banning cigarette advertising and making offices and public places totally tobacco-free.
Bettcher says such actions could save 200 million lives by 2050.
He calls it a completely preventable epidemic.
His comments were made at the start of an international conference in Bangkok to draw up a masterplan to kick the smoking habit globally.