China will have at least 200m obese people within 10 years if current trends continue, the state media say.
Obesity among children rises by 8% annually, the report warns
They quoted a top medical expert as saying high-fat diets and less active lifestyles in a country with rising incomes were exacerbating the problem.
The expert said trends among children were the most worrying with 10% of them considered obese.
China has already 90m people out of 1.3bn whose weight is more than 20% in excess of the accepted level.
TV, computers, cars
The latest trends were analysed in the report by Chen Chaogang, a senior university doctor in Guangdong province.
Chinese are being urged to exercise more
He said that rapidly improving living standards had led to a fast-food culture in many cities and more Chinese were adopting more sedentary lifestyles that centred around television, computers and cars.
Mr Chen's report said the problem was particularly bad among youths, with the number of the obese children increasing by 8% every year.
China's one-child policy means many families have just one boy or girl who receive all the attention they want from parents and grandparents, the BBC's Daniel Griffiths in Beijing says.
He adds that in a country that suffered mass starvation only a few decades ago, it is difficult to persuade those doting adults to give their children just a little bit less to eat.