Action must be taken to prevent an entire generation becoming addicted to nicotine, cardiologists have warned, as they published new research suggesting vaping could damage the brain, heart, blood vessels and lungs.
Experts said young people must not be allowed to get hooked on e-cigarettes, as vaping rates, particularly in the US, continue to rise.
The warning comes after 19-year-old Ewan Fisher, from Nottingham, told how he almost died from serious respiratory failure after vaping.
Lead researcher of the new study, Professor Thomas Munzel, from the department of cardiology of the University Medical Centre in Mainz, Germany, said e-cigarettes are so dangerous, as well as addictive, that countries should consider banning them.
He and his colleagues also argued there is a "paucity of evidence" to support claims that e-cigarettes are a "healthy" alternative to smoking or that they help people quit.
This is in direct contrast to the advice issued by Public Health England (PHE), which stands by its claim that e-cigarettes are 95% less harmful than smoking.
The new study, published in the European Heart Journal, looked at the effect of e-cigarette vapour on blood flow and stiffness in the brachial artery in the upper arm in 20 smokers before they vaped an e-cigarette, and then 15 minutes afterwards.
Some 151 mice were also exposed to e-cigarette vapour over one, three or five days, for 20 minutes six times a day.
The results suggested that just one vaping episode increased heart rates and caused the arteries to stiffen, and that the inner lining of the arteries, the endothelium, stopped working properly in smokers.
In the mice, blood vessels, including those in the lungs and the brain, appeared to become damaged.
Prof Munzel said: "Our data may indicate that e-cigarettes are not a healthy alternative to traditional cigarettes, and their perceived 'safety' is not warranted.
"In addition, we still have no experience about the health side effects of e-cigarettes arising from long-term use.
"The e-cigarette epidemic in the US and Europe, in particular among our youth, is causing a huge generation of nicotine-addicted people who are being endangered by encouragement to switch from traditional cigarettes to e-cigarettes.
"Research like ours should serve as a warning about their dangers, and aggressive steps should be taken to protect our children from health risks caused by e-cigarettes.
"We cannot allow an entire generation to become addicted to nicotine."
Vaping is less risky than smoking
Studies from the US suggest more than 3.6 million children there use e-cigarettes.
In the UK, a report published in February and commissioned by PHE showed that the number of children and young people who are vaping is on the rise.
Some 11.7% of 11 to 18-year-olds in 2018 had tried e-cigarettes once or twice at some point, almost double the 6.5% in 2014.
And 3.4% of those polled in 2018 reported using e-cigarettes currently - more than double the 1.6% in 2014.
Deborah Arnott, chief executive of the charity Action on Smoking and Health, said of the new study: "The short-term effects of e-cigarettes on arterial stiffness are very similar to drinking coffee, taking exercise or watching horror movies.
"While vaping isn't risk free, it's much less risky than smoking, which kills over 250 people a day in the UK.
"Vapers shouldn't be scared back to smoking - that would be a real public health tragedy."
Martin McKee, professor of European Public Health at the London School of Hygiene and Tropical Medicine, said the study was "an excellent piece of detective work".
He added: "This study shows that the concentration of one substance, acrolein, is nine times higher in e-cigarette vapour than in the liquid itself.
"It also uses a series of elegant experiments, using genetically modified mice and drugs to influence metabolic pathways, to show that it is the acrolein that is damaging the functioning of the arteries, producing the same effects in mice and humans.
"This should be a wake-up call for those who, despite growing evidence to the contrary, continue to promote these products."
Tim Chico, professor of cardiovascular medicine at the University of Sheffield, said: "This study... shows clearly that e-cigarettes have negative effects on the cardiovascular system.
"The authors of this study call for countries to consider banning them. This raises a challenging question since a ban at this stage would be in the absence of clear evidence of long-term increases in risk of heart disease.
"However, such evidence will take years to accumulate while people are possibly exposing themselves to harm."
Professor Jeremy Pearson, associate medical director at the British Heart Foundation, said: "E-cigarettes contain far fewer of the damaging chemicals which can cause diseases related to smoking tobacco, but that doesn't mean they are risk free.
"E-cigarettes still contain other chemicals, metals, and flavouring which affect our heart and blood vessel health.
"This study reinforces that vaping should never be taken up by people who don't already smoke and emphasises the need for more research into the long-term impact of vaping on our health."