Baidu Inc, China's biggest Internet company by market value, forecast third-quarter revenue that beat analyst estimates as customers spend more on search-engine advertising in the world's second-biggest economy, Bloomberg reported Tuesday.

Revenue will rise to between 3.95 billion yuan ($613 million) and 4.05 billion yuan in the three months to Sept 30, Baidu said in a statement on Monday. The Beijing-based company's guidance beat all 11 analyst estimates compiled by Bloomberg.

Baidu climbed 8.9 percent in late US trading as the forecast underscored demand for advertising on the company's search-engine service, which is gaining users and extending its lead over Google Inc in China. Chief Executive Officer Robin Li, ranked the nation's richest man by Forbes magazine, is adding services to meet rising competition from Internet rivals including Tencent Holdings Ltd and Alibaba Group Holding Ltd.

Baidu's shares surged as much as $13.97 to $170.51 in extended trading, after closing at $156.54 on the Nasdaq Stock Market. The stock had gained 62 percent this year after more than doubling in 2010, outperforming the Hong Kong-traded shares of Tencent, China's biggest online-games company, and Alibaba.com Ltd, the business-to-business unit of Alibaba Group, the country's biggest e-commerce company.