China has more than 300 million registered microbloggers, state media said Monday, one of its fastest growing groups of internet users that the government has vowed to control.

The country has the most internet users in the world, at 485 million, the official Xinhua news agency said, citing Zhang Xinsheng, an official with the Ministry of Industry and Information Technology.

It also has the world's largest internet infrastructure, Zhang said. The statistics were released during an internet conference in China's central Hubei province.

But authorities are facing challenges in creating a civilized online environment, on social media platforms such as the country's most popular Twitter-like microblogging site Sina Corp's Weibo, the deputy head of the State Council Information Office, Qian Xiaoqian, said.

Beijing has repeatedly criticized microblogs for irresponsibly spreading what it calls unfounded rumors.

Microblogs allow users to issue bursts of opinion -- a maximum of 140 Chinese characters -- that can course through chains of followers who instantly receive messages, challenging censors who have a hard time monitoring the tens of millions of messages sent every day.

Sina has faced increasing regulatory scrutiny, with government officials pressuring the company to better police Weibo, which has become a powerful medium to spread news and opinions and vent frustration against government policies.

China's ruling Communist Party has vowed to intensify control over online social media and instant messaging tools. But analysts say it is unlikely to shut down what has become an important valve for monitoring and easing social pressures.

Sina and other Chinese microblog operators already deploy technicians and software to monitor content and block and remove comment deemed unacceptable, especially about protests, official scandals and party leaders.

China's Internet Network Information Center had said earlier that the number of Chinese users registered on domestic microblog sites reached 195 million by the end of June, a more than threefold increase on the number at the end of 2010.

(Reporting by Michael Martina; editing by Philippa Fletcher)