Vaping - the rise in five charts
Countries including the Seychelles and Brazil have also banned the sale of e-cigarettes, but spending on them globally is going up.
These charts tell the story of a growing industry - but how many people cheap vape deals, how much is being spent on e-cigarettes and why do people buy them?
1. Vaping is increasingly popular
According to the latest statistics from the World Health Organization, there has been a small but steady decrease in the estimated number of smokers globally since 2000 - from 1.14 billion then to about 1.1 billion now.
But it's a different matter when it comes to vaping.
The number of vapers has been increasing rapidly - from about seven million in 2011 to 35 million in 2016.
Market research group Euromonitor estimates that the number of adults who vape will reach almost 55 million by 2021.
2. Spending on e-cigarettes is growing
The e-cigarette market is expanding, as the number of vapers rises.
The global vapour products market is now estimated to be worth $22.6bn (￡17.1bn) - up from $4.2bn just five years ago.
The United States, Japan and the UK are the biggest markets. Vapers in the three countries spent a combined $16.3bn on smokeless tobacco and vaping products in 2016.
European countries such as Sweden, Italy, Norway and Germany also feature in the top 10.
3. Open-system e-cigarettes are the most popular
There are two main types of e-cigarette - open and closed system, also known as open and closed tank.
In an open system, the liquid that is vapourised can be refilled manually by the user. There is also a removable mouthpiece.
Closed system e-cigarettes use ready-made refills, which screw directly on to the e-cigarette's battery.
Since 2011, the gap in spending between them has been gradually widening.
It is reckoned that this year, vapers will spend an estimated $8.9bn on open system e-cigarettes, also known as vape pens - more than double the spend on closed-system products.