The number of Internet users in China, already the world's largest online market, has leapt to 420 million, according to official figures released Thursday.

The figure, almost a third of the population, marks an increase of 36 million -- more than the population of Canada -- since the number of users was last given at the end of 2009.

The fresh figures for the world's most populous nation were released by the China Internet Network Information Centre (CNNIC), a government-linked industry body, and reflect data gathered through the end of June.

Among the factors helping to drive the latest increase was a 31 percent jump in the number of Chinese who shop online, which rose to 142 million, the report said.

The number of users accessing the Internet via mobile phones, meanwhile, jumped to 277 million, up from the centre's earlier estimate of 233 million, helped by the fast expansion of the country's third-generation (3G) network.

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.

The government blocks web content that it deems politically sensitive in a vast system dubbed the "Great Firewall of China".