Health campaigners have broadly welcomed a government move to raise the legal minimum age for buying tobacco in England and Wales from 16 to 18 years.
Shopkeepers fear abuse from youths used to buying cigarettes
The law change will be introduced in October following a ban on smoking in public and work places.
The British Medical Association said it was a step in the right direction but warned it would need proper enforcement and more targeted cessation programmes.
Shopkeepers though fear a backlash from young people refused cigarettes.
In April, smoking in public and work places will be banned in Wales, and by July that ban will be extended to England.
About 9% of 11 to 15-year-olds smoke and ministers hope the law change will reduce this figure.
Announcing the move, Public Health Minister Caroline Flint said: "Smoking is dangerous at any age, but the younger people start, the more likely they are to become life-long smokers and to die early.
"Buying cigarettes has been too easy for under-16s and this is partly due to retailers selling tobacco to those under the legal age."
The government argues raising the legal age to 18 will make it easier for retailers to spot under-age smokers.
Ministers also believe that bringing the legal age for buying tobacco in line with that of alcohol will reinforce the dangers of smoking to young people.
It will also bring England and Wales in line with Canada, Australia, New Zealand and the US.
But James Lowman, a spokesman for the Association of Convenience Stores, said shop owners could face abusive behaviour if they refused to sell tobacco to young people who had previously been legally able to buy it.
"The government needs to dedicate real resources to public education to prevent this happening," he said.
"Customers need to know they may be asked to prove their age when buying a restricted product like tobacco."
Dr Vivienne Nathanson, head of science and ethics at the British Medical Association (BMA), said far more needed to be done to discourage children from smoking.
"Increasing the age limit to 18 would be a step in the right direction.
"However, the new limit is only going to be effective if it is properly enforced and part of a broad set of actions designed to discourage young people from starting to smoke."
Dr Nathanson called for more targeted smoking cessation programmes and action to tackle the way that the entertainment industry still portrayed smoking as a cool thing to do.
A recent survey suggested that only 23% of children aged under 16 who tried to buy tobacco found it difficult to do so.
Evidence shows that nearly 70% of 11 to 15-year-old smokers say they buy their cigarettes from small shops such as newsagents and corner shops.