New rules banning junk food advertising across media targeting children are coming into effect.
Highly fatty, sugary and salty foods will no longer be advertised across non-broadcast media targeting under-16s as of Saturday.
The new regulations are part of a drive to tackle rising levels of childhood obesity in the UK.
The changes mean that media such as print, cinema, online and social have now been brought into line with television - where strict regulations prohibit advertising unhealthy food to children.
TV-like content online, such as on video-sharing platforms or 'advergames', must also adhere to the new rules.
The Committee of Advertising Practice explained that shifting media habits among young people and evolving advertising techniques had fundamentally changed children's relationship with media.
Latest Ofcom figures show that young people aged between five and 15 now spend about 15 hours each week online, overtaking the time they spend watching a TV set.
CAP chairman James Best said: "These measures demonstrate the advertising industry's continuing commitment to putting the protection of children at the heart of its work.
"The new rules will alter the nature and balance of food advertising seen by children and play a meaningful part in helping change their relationship with less healthy foods."
The Food and Drink Federation said the industry group "fully supported" the "landmark move".
However, the Obesity Health Alliance argued that the new rules were only a "small step in the right direction".