The figure was reported by Xinhua news agency, quoting the Ministry of Information Industry, but AFP was not able to independently confirm the data.
It represents a marked increase from the end of 2007, when the number of online users stood at 210 million, just five million less than the US, according to figures released by the China Internet Network Information Centre.
BDA China, a Beijing-based research firm, last month also said China had overtaken the US in the number of web surfers, and was expected to have 280 million internet users by the end of the year.
"Despite rapidly increasing the internet population, the proportion of internet users among the total population is still lower than the global average level," Xinhua news agency said, quoting the ministry.
The proportion came to 16 per cent at the end of 2007, compared with a world average of 19.1 per cent, the news agency said.
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China already has the globe's biggest mobile phone user population, numbering 540 million at the end of November last year, according to government figures.
The fast growing online population has made the internet a new forum for the average Chinese to express opinions in a free-wheeling way rarely seen on the strictly government-controlled traditional media.
It has stirred up Beijing's fears about potential social unrest, and President Hu Jintao called last year for efforts to "purify" the internet.