BEIJING — Tens of thousands of underground Internet cafes will be targeted in a four-month government crackdown designed to stop teenagers accessing harmful and violent content.

Internet cafes located in rural areas, suburbs and areas around middle and primary schools are the main targets of the campaign.

“Illegal Internet bars are harming left-behind rural teenagers that lack parental care because their parents are away trying to make a living in cities,” Zhou Yongping, deputy director of the State Administration for Industry and Commerce, said in remarks carried on national media.

China has 316 million netizens, the biggest online population in the world.

The number of illegal Internet cafes is growing because of demand, the limited number of legal outlets, limited access to the web and a lack of enforcement. Illegal Internet cafes make large profits because they have much lower costs compared with registered outlets. Underground Internet bars also often have poorer quality computers, so even if they have many terminals the businesses are still cheaper to operate.

Zhou said last year his org cracked down 13,000 illegal Internet cafes. In the five years leading up to 2008, his department had cracked down on nearly 130,000 illegal Internet bars.

By March 2007, according to official data, China had over 110,000 legal Internet bars. This compares with around 150,000 legal Internet cafes.

“There is also a trend of more illegal Internet bars appearing in urban-rural joint areas and city communities,” said Zhou.

The campaign, which will run from June 1 until Sept. 30, has some high-profile backers in the government. It will involve Zhou’s administration as well as the ministries of public security, culture, and industry and information technology, and the civilization office of the Central Committee of the Communist Party of China.

Zhou said local authorities would confiscate facilities and equipment belonging to illegal businesses, instead of simply punishing violators with fines. Those found violating laws would also face criminal punishment.

Rules introduced in 2004 require the owners of registered Internet cafes to have a minimum of 1 million yuan ($146,000) in the bank, 200 computers and an operating area of more than 300 square meters.