China's state news agency has called for a crackdown on what it calls the spread of toxic rumors over the Internet.

In an article Tuesday, published only in Chinese, Xinhua criticized the increasingly popular social networking sites for spreading rumors like cancer, and urged preventive action.

The Xinhua article comes just days after a senior Communist Party official visited China's top Internet companies and urged them to stop the spread of what he termed harmful information.

China has the world's largest online population with close to 500 million users that increasingly use blogs to spread news, develop public debate and uncover scandals.

Chinese authorities use sophisticated software to try to control what is said on the Internet. The government has become increasingly nervous about the Arab uprisings, which have gathered huge support through online networking. Officials fear they may inspire unrest in China.

Most recently, users of China's Weibo service, the country's equivalent to Twitter, sent millions of messages criticizing the official response to the high-speed train disaster in July, which killed 40 people.

The development has exposed the difficulty of controlling the spread of information.