Films showing smoking should be given an adult rating to protect children from the tobacco industry, the World Health Organisation (WHO) has said.
In a new report, it called on governments to do more to prevent children and adolescents from one of the "last" frontiers in tobacco promotion.
"Movies showing use of tobacco products have enticed millions of young people worldwide to start smoking", the WHO said in a statement.
Dr Douglas Bettcher, WHO's director for the department of prevention of non-communicable diseases, added: "With ever tighter restrictions on tobacco advertising, film remains one of the last channels exposing millions of adolescents to smoking imagery without restrictions.
"Smoking in films can be a strong form of promotion for tobacco products."
In 2014, the US Centres for Disease Control and Prevention estimated that in the United States alone, exposure to on-screen smoking would recruit more than six million new, young smokers.
Of these, two million would ultimately die from diseases caused by tobacco, the figures suggested.
In 2014, smoking was found in 44% of all Hollywood films, and 36% of films rated for young people.
Dr Armando Peruga, from the WHO's tobacco-free initiative, said: "We saw for a while a decrease in the tobacco incidences in films and other entertainment productions.
"But based on what we monitored, we saw in 2013/14 a turning point - a picking-up of the number of tobacco scenes.
"The tobacco industry has been looking at alternatives to promote their products and film is the last frontier for tobacco companies.
"In some films, the percentage of tobacco scenes is far greater than you would see in the society in which the film is set."
The British Board of Film Classification (BBFC) said the last review of its guidelines, in 2013, involved more than 10,000 members of the public from across the UK.
"The public agrees that the classification of smoking in films should be proportionate and reflective of UK laws, for example, a scene of an adult smoking in a film should not instantly require an 18 classification," the BBFC said in a statement.
"However, glamorisation of smoking in works that appeal to children is more likely to receive a higher classification."