The number of web users in China has surged to 618 million, a government agency says, underscoring the rapid growth of online connectivity in the country with the world's largest internet population.

Its online population - defined as those who have used the internet at least once in the past six months - rose by more than 53 million in 2013, the China internet Network Information Centre (CNNIC) reported.

As many as 500 million people in China were accessing the internet using mobile phones by December, the report added.

China already had more web users than any other country in the world. It is home to a huge e-commerce market and the web has been used by citizens to spotlight government abuses, creating a concern for the ruling Communist party.

China maintains tight controls over the internet, blocking websites it deems politically sensitive in a system dubbed the "Great Firewall of China" and encouraging social media companies to censor user-generated content.