The World Health Organization has called for strict regulation of electronic cigarettes and bans on indoor use, advertising and sales to minors, in the latest bid to control the booming new market.
In a long-awaited report, the United Nations health agency also voiced concern at the concentration of the $3bn market in the hands of transnational tobacco companies.
The report will be debated by member states at a meeting in October in Moscow.
"In a nutshell, the WHO report shows that e-cigarettes and similar devices pose threats to public health," Douglas Bettcher, director of the agency's department on non-communicable diseases, told a news briefing in Geneva.
The uptake of e-cigarettes, which use battery-powered cartridges to produce a nicotine-laced vapour, has rocketed in the past two years.
Their risks are the subject of debate.
Because they are so new, there is a lack of long-term scientific evidence to support their safety and some fear they could be a "gateway" to nicotine addiction and tobacco smoking.
The European Union has already agreed to requirements around advertising and packaging to ensure the safety and quality of e-cigarettes.
The US Food and Drug Administration has proposed banning sales to anyone under 18 but no curbs on advertising.
The WHO launched a public health campaign against tobacco a decade ago, clinching the WHO Framework Convention on Tobacco Control.
Since entering into force in 2005, the health treaty has been ratified by 179 states, although not the United States.
The treaty recommends price and tax measures to curb demand as well as bans on tobacco advertising and illicit trade in tobacco products.
Prior to today’s report the WHO had indicated it would favour applying similar restrictions to all nicotine-containing products, including smokeless ones.
In the report, the WHO said there are 466 brands of e-cigarettes and the industry represents "an evolving frontier filled with promise and threat for tobacco control".
It urged a range of regulatory options, including banning vending machines in most locations and preventing e-cigarette makers from making health claims such as that they help people quit smoking, until there is hard evidence.
Smokers should use a combination of already-approved treatments for kicking the habit, it said.
While e-cigarettes are likely less toxic than conventional ones, the WHO dismissed the idea that e-cigarettes merely produced "water vapour", arguing they exposed bystanders and non-smokers to nicotine and other toxicants.
Their use also posed a threat to adolescents and the foetuses of pregnant women, it said.
One concern is that e-cigarettes may tempt children, and the report called for a ban on flavours until there was proof they did not attract adolescents.
E-cigarettes can be customised with flavours ranging from bacon to bubble gum.
Scientists are divided on the risks and potential benefits of e-cigarettes.
One group of researchers warned the WHO in May not to classify them as tobacco products, arguing that doing so would jeopardise an opportunity to slash disease and deaths caused by smoking.
Opposing experts argued a month later that the WHO should hold firm to its plan for strict regulations.
Major tobacco companies including Imperial Tobacco, Altria Group, Philip Morris International and British American Tobacco are increasingly launching their own e-cigarette brands as sales of conventional products stall in Western markets.
The American Heart Association said in a report yesterday that it considered e-cigarettes that contain nicotine to be tobacco products and therefore supports their regulation under existing laws on the use and marketing of tobacco products.
"Although the levels of toxic constituents in e-cigarette aerosol are much lower than those in cigarette smoke, there is still some level of passive exposure," the AHA said.