In order to tackle a "ticking timebomb" of child obesity, Khan has launched a proposal to ban ads for foods that are high in fat, salt or sugar across the entire Transport for London network.
The plans are part of the Khan’s draft London Food Strategy, published today.
Khan said: "Child obesity in London is a ticking timebomb and I am determined to act. If we don’t take bold steps against it we are not doing right by our young people as well as placing a huge strain on our already pressurised health service in years to come.
"It can’t be right that in a city as prosperous as London that where you live and the income you have can have a massive impact on whether you have access to healthy, nutritious food and your exposure to junk food advertising."
London has one of the highest child overweight and obesity rates in Europe, with almost 40% of children aged 10 or 11 being overweight or obese, the mayor’s office added.
A ban on junk foods ads would follow restrictions on HFSS ads aimed at children, which came into force in the UK last year. Ads that directly or indirectly promote HFSS products are no longer supposed to appear in media aimed at children under 16, or where children under 16 make up at least 25% of the audience.
Barely a month after being elected Mayor of London in 2016, Khan announced a ban on ads that are seen to promote unhealthy or unrealistic body types.