For the past decade, Huang Qing has seen her girth expand at a startling rate.

"My waistline has already grown past the tape measure," said the 17-year-old in Shanghai. Her weight has rocketed from 140 kg to 210 kg in the past four years, four to five times the weight of most her age.

Wearing a loose, red T-shirt and black sweatpants that take "three times" the usual amount of cloth to be tailor-made, Huang has to drag her legs very slowly to move about in her home.

"To be frank, I even find it difficult to get up from the bed," she said.

Huang's weight has increased so much that she has crushed four chairs at home, and many more at her relatives'.

To avoid such "calamities", the girl has to spend the majority of the day lying on her bed or surfing the Internet. She also quit vocational school two years ago, and is unwilling to walk outside her home - both in fear of being scorned and because of a lack of energy, said her mother, Jin Ming.

"No one is sure how she got like this. She does not eat that much but after the age of 6, she just kept on ballooning without obvious reason," Jin said.

In the family battle against the bulge, Jin said they had tried every means possible to help Huang lose weight. They tried acupuncture, diet pills, swimming and judo.

But nothing worked.

While youth such as Huang may be an extreme case of childhood obesity, its prevalence among adolescents is on the rise in the country. Overall food availability has increased due to rising affluence and children are leading a more sedentary lifestyle, especially in cities. National surveys on the health of schoolchildren showed that the prevalence of obesity among children between 7 and 18 had increased four times from 1985 to 2000.

And figures for the number of overweight children in the same age range and time period had increased 28 times.

Qu Shen, a doctor from Shanghai No 10 People's Hospital, said the increased rate of childhood obesity in China in the past 10 years has even surpassed that of the United States in the past 5 decades.

Along with expanding waistlines, being overweight or obese increases the risk of type-2 diabetes and heart disease, which used to be adult diseases but are growing increasingly common among children, he said.

Luckily for her, Huang Qing has not turned away from being the happy and optimistic girl she has always been, said Jin.

"Isn't she wonderful? She wears a smile that is rarely seen in a girl of her size," she said.

Huang reaffirmed that view. "I do get sad sometimes when losing weight seems so hopeless to me but for most of the time I know I won't lose anything being happy," she said. "We are looking for a good doctor—I think one day I will become healthy again."