"Vaping" can help traditional cigarette smokers kick the habit or at least cut down, a study has found.

The UK and New Zealand researchers behind the Cochrane Library review say the results are encouraging but that more studies are needed.

Electronic cigarettes work by vaporising a solution that usually contains nicotine.

The review drew on data from 662 smokers across two randomised trials, and found that about 9% of those who used electronic cigarettes were able to quit smoking by the one-year mark - more than twice the rate of those using nicotine-free placebo devices.

Among people who did not quit, 36% of those smoking e-cigarettes cut down on the number of cigarettes they were smoking by half, while 28% of those using the placebo devices were able to halve their cigarette consumption.

One of the review's authors, clinical psychology professor Peter Hajek, said his team was limited by the small number of trials already available and the sample sizes in each.

"I think they should be used, but not as the first line of treatment. I think the smoker who is looking for help stopping smoking should be given treatments which have been proven clearly effective," he said.

Deborah Arnott, chief executive of health charity Action on Smoking and Health, said the review showed e-cigarettes could play a role in helping smokers quit.

She said: "It should stimulate more research, which is just what is needed in this important area of public health which has the potential to save so many lives."