Britain is to ban the sale of electronic cigarettes to children under 18, citing possible adverse health effects and outlining a need for further research.
E-cigarettes are puffed like a regular cigarette but deliver nicotine by vaporising liquid rather than burning tobacco. They have grown in popularity and some analysts predict the market could outpace that for conventional cigarettes within a decade.
"We do not yet know the harm e-cigarettes can cause to adults, let alone to children, but they are not risk- free," Chief Medical Officer Sally Davies said.
She said e-cigarettes could produce toxic chemicals and that variations in the strength of the nicotine solutions meant they could end up being "extremely damaging" to young people's health.
The global market for e-cigarettes was estimated at more than US$2 billion last year by market consultant Euromonitor.
Sunday's announcement included plans to make it illegal for adults to buy regular cigarettes for people under 18.
The changes will be written into a bill already on its way through Parliament and are expected to have cross-party support, although the opposition Labour Party criticised the government for not acting more quickly.
The battery-powered metal tubes of e-cigarettes are seen as less harmful than regular cigarettes and a useful way to wean smokers off their habits. But critics say they can act as a gateway to nicotine addiction and that more research is needed on the health implications.
Regulators in Europe and the US have been debating policy towards the industry. The European Union reached an agreement last month to allow e-cigarettes to be sold as consumer products rather than more tightly regulated medical devices.