The move was welcomed by the Obesity Health Alliance (OHA) and the British Heart Foundation (BHF).
Caroline Cerny, from OHA, said: “Junk food advertising works – it can successfully influence our day-to-day choices.
“That’s why food companies spend hundreds of thousands every year, to ensure that their unhealthy products remain in the spotlight.”
Jacob West from BHF added: “Ending the constant flood of online junk food advertising would be a big step forward in protecting everyone’s health, particularly children.
“This must be implemented swiftly alongside a 9pm junk food marketing watershed on TV and a comprehensive set of other measures to create a healthy environment.”
However, plans have been criticised by campaigners, and the Food and Drink Federation said it “beggars belief” the industry had only been given six weeks to respond.
Head of UK diet and health policy Kate Halliwell said: “It could not come at a worse time for food and drink manufacturers – the industry is preparing for its busiest time of the year and working flat out to keep the nation fed through lockdown, all while facing down the very real threat of a no-deal Brexit.”
Advertising campaigners said the plans would also deal a “huge blow” to a sector already dealing with the impact of Covid-19.
In a joint statement, the leaders of the Advertising Association, the Incorporated Society of British Advertisers, the Institute of Practitioners in Advertising and the Internet Advertising Bureau UK said: “To borrow the Prime Minister’s language, this is not an ‘oven-ready’ policy; it is not even half-baked.
“But it does have all the ingredients of a kick in the teeth for our industry from a Government which we believed was interested in prioritising economic growth alongside targeted interventions to support health and wellbeing.”