The number of internet users in China, already the largest in the world, has surpassed 400 million and accounts for almost a third of the country's population, state media reported.

The online population in the world's most populous nation has reached 404 million, the official Xinhua news agency said, citing the State Council Information Office. That compares with 384 million users at the end of last year.

Users accessing the internet with mobile phones was steady at 233 million while the number of people with broadband access reached 346 million, the report said.

China's spiralling online population has turned the internet into a forum for citizens to express their opinions in a way rarely seen in a country where the traditional media is under strict government control.

The growing strength and influence of the web population has prompted concern in Beijing about the internet's potential as a tool for generating social unrest, and authorities have stepped up surveillance in recent years.