Switching to e-cigarettes could save millions of smokers' lives, a conference on the increasingly popular devices heard, though some experts warned more research on the health effects is needed.
The merits of e-cigarettes were thrashed out at a one-day gathering of 250 scientists, policymakers, industry figures and enthusiasts at the Royal Society in London on Tuesday.
The use of electronic cigarettes - battery-powered devices that simulate smoking by heating and vaporising a liquid solution containing nicotine - has grown rapidly, with tobacco manufacturers jumping on the trend.
Many delegates merrily "vaped" away through the indoor conference sessions, including one man puffing on a large e-pipe and another inhaling an e-cigar that lit up blue.
"Cigarettes are killing 5.4 million people per year in the world," said Robert West, a health psychology professor and the director of tobacco studies at Cancer Research UK.
He told delegates that switching to e-cigarettes could save millions of lives, but the debate was about "whether that goal can be realised and how best to do it".
The professor said almost a third of attempts to quit smoking involved e-cigarettes.
Deborah Arnott, chief executive of the Action on Smoking and Heath (ASH) pressure group, said e-cigarettes had "significant potential" and were "a lot less harmful than smoking".
But she warned: "The tobacco companies are moving in. For them it's potentially a 'Kodak moment' because if everyone moved to e-cigarettes, they'd lose their market. So they've got to be in there. A lot of the bigger e-cigarette companies have already been bought up."