E-cigarettes are almost twice as effective at helping smokers quit as nicotine replacement treatments like patches, lozenges and gum, according to the results of a major clinical trial.

The study, involving almost 900 smokers, found that 18 percent of e-cigarette users were smoke-free after a year, compared to 9.9 percent who tried quitting using other products.

"This is great news for cigarette smokers who want to quit," said Richard Miech, from the University of Michigan in the United States who has studied e-cigarettes but was not involved in this trial. "This evidence is persuasive."

E-cigarettes have no tobacco, but contain nicotine-laced liquids that the user inhales in a vapour. Many big tobacco companies, including British American Tobacco, Imperial Brands and Japan Tobacco, sell e-cigarettes.

Using e-cigarettes, or "vaping", is considered by many health experts to be an effective way for smokers to give up tobacco, but the scientific community has been divided over their potential public health benefits.

Independent experts said the latest trial, funded by Britain's National Institute for Health Research and carried out by researchers from Queen Mary University of London, was robust and well-conducted.

Some research has previously suggested e-cigarettes might help smokers cut back or quit altogether, but other studies have raised concerns about their use among teenagers.

This study, published in the New England Journal of Medicine, found a stronger e-cigarette effect than previous trials. The researchers said this might be due to the inclusion of smokers seeking help, the provision of face-to-face support, and allowing the e-cigarette users to choose their own liquids.

In the trial, 886 smokers were randomly divided into groups to receive either up to three months' supply of nicotine replacement products such as patches, gum, lozenges and sprays, or an e-cigarette starter pack with one or two bottles of liquid and encouragement to buy their own choice of future supplies.

All participants were also tested to see if they were still smoking tobacco cigarettes, and had weekly one-to-one support for at least four weeks. The researchers said one reason e-cigarettes were found to be more effective may be that they allow for better tuning of nicotine doses to individual needs.

Jamie Hartmann-Boyce, a behavioural expert at Britain's Oxford University, said the study adds to growing evidence that e-cigarettes can improve health by helping smokers quit.

"More research is needed on the effects of long-term electronic cigarette use, but experts agree e-cigarettes are considerably less harmful than smoking, so switching...is likely to bring substantial health gains," she said.