New York Mayor Michael Bloomberg and Microsoft co-founder Bill Gates have pledged $375 million to fight what they called a global tobacco epidemic.
The billionaires said the money would go to anti-smoking groups working with governments of developing countries such as India and China to curb tobacco use.
Mr Bloomberg, who championed New York City's groundbreaking smoking ban in 2002, is adding $250 million over four years to a programme he started several years ago that has $125 million committed to it.
The Bill & Melinda Gates Foundation will invest $125 million over the next four years.
"Smoking is an epidemic that can be stopped, and we want more people to get involved," Gates said at his first public event as chairman of his philanthropic foundation since he left his full-time executive role at Microsoft in June.
Statistics show that by 2030, more than 80 per cent of worldwide tobacco-related deaths will occur in low- and middle-income countries compared to half today.
Mr Bloombery and Mr Gates pointed to declining US smoking rates since bans, including those in bars and restaurants, were introduced in California and New York. Nations such as Ireland, France, Italy and Turkey have followed suit.
They said poor nations could use government-backed incentives, such as higher taxes on tobacco and bans on advertising, promotion and sponsorship.
Mr Bloomberg noted difficulties in places such as China, where the government owns cigarette manufacturing companies.
"What we have to show them is that the revenue they get, the profits they get from selling cigarettes, are dwarfed by the expense to society," Mr Bloomberg said.
China has an estimated 350 million smokers, a third of the world's total, and 1 million people die from tobacco there each year, according to the World Health Organization.
Beijing plans to ban smoking in sports venues, parks and public transport during next month's Olympic Games, but restaurants and hotels are exempted.
Reuters