Junk food manufacturers should be banned from targeting unhealthy products at children, say public health doctors.
Unhealthy eating is a big problem
The BMA's Annual Conference of Public Health Medicine called on ministers to ban television advertising of junk foods before the watershed.
Doctors said a ban was essential to protect children's health.
The government is due to unveil a White Paper setting out measures to tackle growing obesity rates later this year.
But Culture Secretary Tessa Jowell has already said ministers favour voluntary action by the food and advertising industry.
She told a Commons Health Committee inquiry into obesity she did not want to "leap to regulation".
Dr Peter Tiplady, chairman of the BMA's Public Health Committee, said: "Children are being bombarded with adverts for products that are extremely bad for their health.
"Food manufacturers are deliberately targeting them by using sports personalities to send out the message that junk food and fizzy drinks will make them more popular."
Dr Tiplady said an integrated approach involving everybody from the government, to local authorities and schools was the only way to tackle the problem of obesity.
He said: "It's easy to say that obesity is a matter of personal choice, but often that's not true for children.
"Schools should allow children to eat healthily and get enough exercise, but many have sold off their playing fields, installed junk food vending machines, and failed to provide healthy school meals.
"If we're going to prevent a major public health crisis we need a joined up approach. Schools and local authorities have a huge responsibility but they need enough funding to be able to provide safe playing areas and healthy food."
Dr Kailash Agrawal, who chaired the conference, described childhood obesity as a "public health timebomb".
He said: "If the government ignores it we will see huge increases in diabetes, strokes, cancer and heart disease - obesity has the potential to cause the same devastation as smoking."
Dr Steve Watkins, deputy chairman of the committee, described the targetting of children with high fat, high salt and high sugar fods as a "pernicious process".
He said: "It is utterly and fundamentally wrong that the food industry, or any other kind of industry, should assume the right, for no more than their own commercial purposes, to persuade people to harm themselves.
"This is especially true of children."
But Dr Watkins was sceptical that a voluntary ban would have any effect.
He said: "Why would the industry take voluntary action when these methods are what commercial success is based on?"