China has said it will launch a six-month crackdown on rampant online gambling, saying the growing industry was causing large flows of money out of the country.

Gambling has been outlawed in China since the Communist Party came to power in 1949, but that has not stopped a thriving underground industry.

The campaign, which will last until August, will be carried out by eight government agencies including the Ministry of Public Security, central bank and the Ministry of Industry and Information Technology.

Online gambling "has caused large cash outflows from the country and seriously disturbed social and economic order," said a statement posted on the public security ministry's website.

The campaign aims to "bust a number of syndicates from home and abroad that collude to organise gambling activities on the Internet and severely punish the illegal rings," it said.

Authorities will also clamp down on underground banks and third-party payment platforms that provide cash transfer services for gambling sites, as well as internet operators that provide web access services, it said.

"(We) will clean up gambling information and websites across the board," the statement said.

The campaign is the latest in a number of steps the government has taken to strengthen control over internet use, which is expanding at a dizzying pace in China.

China has the world's largest online population with at least 384 million users, according to official figures.

The government censors the web to curb what it considers "unhealthy" content including porn and violence - using a system known as the "Great Firewall of China."