BEIJING, Sept 4 (Reuters) - The vast majority of Chinese schoolchildren chose to stay home and surf the Internet during the summer holidays rather than play outside, state media said on Tuesday, citing a survey.

The poll of 103 children aged 4 to 14 found that just 4 percent chose to do outdoor activities during the holidays and only 9 percent took part in summer educational camps.

School began again across China on Monday.

"Five years ago, when the Internet was not so popular among students, they preferred going out during summer holidays. Nowadays they prefer to stay at home and play Internet games," a medical official was quoted as saying by the China Daily.

About 13 percent of China's 20 million Internet users under 18 are classed as addicts, state media have reported.

In Shanghai last month, local authorities launched an experimental summer camp for 40 youngsters to try to wean them of their addiction.

China is also so worried about growing obesity in its children, thanks to the sedentary lifestyle and unhealthy Western-style fast food, it recently instructed schools to make dancing lessons compulsory in a bid to shed some pounds.