BEIJING — China has surpassed the United States to become the world’s largest Internet-using population, reaching 221 million by the end of February, state media said on Thursday. The number of Internet users in China was 210 million at the end of last year, only 5 million fewer than the U.S. Internet users then, Xinhua news agency said, quoting the China Internet Network Information Centre. ‘Despite a rapidly increasing Internet population, the proportion of Internet users among the total population was still lower than the global average level,’ Xinhua quoted the Information Ministry as saying. The proportion was 16 percent at the end of 2007, compared with 19.1 percent for the world average. Internet censorship is common in China, where the government employs an elaborate system of filters and tens of thousands of human monitors to survey surfing habits, surgically clipping sensitive content. But the Internet has most recently become an important tool in countering anti-China protest dogging the Olympic torch relay with an outpouring of nationalism and indignation.