New international research estimates that passive smoking leads to 600,000 deaths around the world, each year.

The World Health Organisation study is the first to assess the global impact of inhaling other people's tobacco smoke.

It found that children are the group most heavily exposed to second-hand smoke, and amount to about a third of the annual death toll.

Among non-smokers worldwide, 40% of children, 35% of women and 33% of men were exposed to second-hand smoke in 2004, the most recent year for which data was available across the 192 countries examined.

When added to the 5.1m fatalities attributable to active smoking, the final death toll from tobacco for 2004 was more than 5.7m people, the study, published in the British medical journal The Lancet, concluded.

Currently, only 7.4% of the world population lives in areas with serious smoke-free laws, and even in these jurisdictions compliance is spotty.

Where laws are enforced, exposure to second-hand smoke in high-risk settings such as bars and restaurants is cut by 90%, earlier research has shown.

Anti-smoking regulations also lower cigarette consumption, and improve people's chances of kicking the habit.

The researchers recommend fully applying the WHO's Framework Convention on Tobacco Control, which includes tobacco tax hikes, advertising bans, and the use of nondescript packaging.