A letter signed by more than 50 researchers and public health specialists is urging the World Health Organization (WHO) to "resist the urge to control and suppress e-cigarettes".
The letter says: "These products could be among the most significant health innovations of the 21st Century - perhaps saving hundreds of millions of lives.
"If regulators treat low-risk nicotine products as traditional tobacco products... they are improperly defining them as part of the problem.
"Regulators should avoid support for measures that could have the perverse effect of prolonging cigarette consumption.
"We are deeply concerned that the classification of these products as tobacco will do more harm than good.
"The potential for tobacco harm reduction products to reduce the burden of smoking-related disease is very large."