The number of people who have tried e-cigarettes almost doubled in two years, a new study shows.
Researchers examined the use of the devices across the European Union between 2012 and 2014.
The team, from Imperial College London, found that in the UK the proportion of people who had tried an electronic cigarette increased from 8.9% to 15.5%.
Across the EU there was an average increase of 7.2% to 11.6%, according to the study, published in the journal Tobacco Control.
The authors used data from 53,000 people in the EU. They found that the country with the highest e-cigarette use was France, with one in five people saying they had tried them.
The nation with lowest number of people who had tried an e-cigarette was Portugal.
Lead author Dr Filippos Filippidis from the School of Public Health at Imperial said: "This research shows e-cigarettes are becoming very popular across Europe - with more than one in 10 people in Europe now having tried one of the devices.
"However there is debate about the risks and benefits associated with e-cigarettes. For instance we don't know whether we may start to see diseases emerge in 10-20 years' time associated with some of the ingredients.
"We urgently need more research into the devices so that we can answer these questions."
The research also showed the proportion of people across the EU who considered e-cigarettes dangerous had also nearly doubled, from 27%t to 51%.
"This analysis of the most up-to-date data from the whole of the EU shows that although perceptions that e-cigarettes are harmful are increasing, levels of those who ever use them are also increasing," the authors wrote.
There has been much debate among scientists and health policy experts over the devices.
A recent report by the Royal College of Physicians concluded that e-cigarettes are likely to benefit the health of the nation. The report's authors suggested that e-cigarettes should be widely promoted as a substitute for smoking.
There is a possibility that the devices may result in some long-term harm because of the inhalation of the ingredients other than nicotine - but the harm that could be caused is substantially smaller than that caused by smoking, the authors said.
Commenting on the latest study, Dr Ram Moorthy, deputy chairman of the British Medical Association's Board of Science, said: "Electronic cigarettes have become increasingly popular since mid-2000, yet there is still a lack of robust research and evidence on their long-term safety.
"This report highlights the need for a strong regulatory framework to ensure that all products on the market are safe and effective as an aid to helping smokers cut down or quit."
Dr Penny Woods, chief executive of the British Lung Foundation, added: "We know that many people are using e-cigarettes to help them quit the much more harmful practice of smoking, including people with lung conditions.
"For them, quitting tobacco is often the single most important thing they can do to turn their health around. We therefore support calls for more research into vaping, we need to be clear on whether e-cigarettes are a safe way of helping them quit".
Rosanna O'Connor, director of drugs, alcohol and tobacco at Public Health England, said: "The evidence is clear, vaping carries a fraction of the risk of smoking yet many smokers are still not aware. This could be keeping people smoking rather than switching to a much less harmful alternative.
"The best thing a smoker can do, for themselves and those around them, is to quit completely, now and forever. E-cigarettes are the most popular means of quitting and NHS stop smoking services are the most effective. By combining the two, smokers have a very good chance of success."
Deborah Arnott, chief executive of health charity ASH, said: "Of more concern is the misperception that using e-cigarettes is harmful. Smokers who have been put off vaping by concerns about safety should be reassured that by switching to e-cigarettes they can improve both the quality and length of life."