The fast spreading e-cigarettes are undoing the anti-smoking efforts of the last three decades, health experts warn.

Also, the number of people being poisoned by e-cigarettes in the US has gone up manifold in the last few years, according to official reports.

The number of calls to poison centres in the US relating to e-cigarettes has risen from one per month in September 2010 to 215 per month in February 2014.

The figures, from the Centres for Disease Control and Prevention (CDC), also show the number of calls per month relating to conventional cigarettes did not increase in the same way.

The CDC statistics show that more than half of the calls relate to children under the age of five.

Poisoning related to e-cigarettes involves the liquid containing nicotine used in the devices.

"This report raises another red flag about e-cigarettes -- the liquid nicotine used in e-cigarettes can be hazardous," CDC director Tom Frieden said in a statement.

E-cigarette liquids come in candy and fruit flavours that are appealing to children.

"The most recent National Youth Tobacco Survey showed e-cigarette use is growing fast, and now this report shows e-cigarette related poisonings are also increasing rapidly," Tim McAfee, director of CDC's office on smoking and health, was quoted as saying.

The study comes close on the heels of news that the Welsh government might include e-cigarettes under the smoking ban.