China's top search engine, Baidu Inc, beat Wall Street's earnings estimates as its revenue grew more than 80 percent year-on-year in the fourth-quarter.

Shares of Baidu were up more than 2 percent to $144.98 in after-hours trade on Thursday.

Baidu said it expects first-quarter revenue of $666.5 million to $688 million. Analysts polled by Thomson Reuters I/B/E/S were looking for revenue of $678.8 million.

The guidance is inline, but people think that considering the (economic) environment and the early Chinese new year, maybe the company is giving conservative guidance, said Qi Guo an analyst at ThinkEquity.

Baidu has expanded its dominant position in China's Internet search market ever since Google Inc decided in 2010 to relocate its search engine to Hong Kong following a standoff with the Chinese government over Internet censorship.

In the fourth quarter, China's online search market grew 70.2 percent to 568 billion yuan, according to technology consulting firm iResearch. For 2011, Baidu had a 76.1 percent share of the market, while Google had 19.8 percent.

Baidu reported fourth-quarter net income of $326.3 million, or 93 cents per American depositary share. Analysts, on average, were looking for earnings of 91 cents per ADS, according to Thomson Reuters I/B/E/S .

Baidu's revenue came in at $710.9 million, a hair above the average analyst expectation of $708.8 million. At this time last year, Baidu reported revenue of $371.3 million.

With more than half a billion users, China is the world's largest Internet market. Yet, Internet penetration is only at 38.3 percent and user sophistication outside the big cities remains low.

Baidu has made efforts to expand into mobile, travel and online video sectors to boost growth. Baidu is also in the midst of launching its own browser, Baidu Liuluanqi.

Shares of Baidu have gained more than 17 percent since the start of the year, but remain off their 52-week high of $165.96.

(Reporting By Alexei Oreskovic, with additional reporting by Melanie Lee; Editing by Steve Orlofsky)