The number of people vaping in the UK has reached 3.6 million - about half the number of smokers - figures from Action on Smoking and Health suggest.
The data indicates most vapers are former smokers, with the main reason for using e-cigarettes being to give up tobacco.
The findings come as the US continues to investigate a spate of serious lung injuries linked to vaping.
India, meanwhile, says it will ban e-cigarettes as they pose a health risk.
E-cigarettes allow users to inhale nicotine in vapour rather than breathing in smoke.
The anti-smoking charity Action on Smoking and Health has been monitoring trends in their use since 2012.
Its latest report suggests vaping helped an extra 70,000 people quit smoking in 2017.
It says the number of vapers in the UK has gone from 700,000 in 2012 to 3.6 million in 2019 - and of these: