Qihoo quickly responded by leading all Baidu-related search requests to cached pages, which mostly have outdated content and awkward typesetting.

"The conflict will compromise users' experience, although it may fuel the development of the industry in the long run," said Dong Xu, an analyst at research firm Analysys International.

Kai-Fu Lee, the Internet veteran and former president of Google China, criticized both companies on his micro blog, saying the losers in the conflict are Chinese netizens.

In response, Zhou Hongyi, Qihoo co-founder and CEO, said Baidu has monopolized the online search industry and threatened the industry and Internet users.

Qihoo's ambition in online searching was inherited from Zhou. In 1998, he set up the first Chinese-language search website, 3721.com. The site was purchased by Yahoo Inc in 2003.

On Aug 21, Qihoo decided to use its default search engine on all of its browsers, replacing Google and Baidu. Qihoo announced five days later that its search engine had lured about 10 percent of the search traffic, and proclaimed itself the second-largest Web search provider in the nation after Baidu.

Zhou's idea of entering the Web searching market is likely to boost the company's revenue in the future, given Qihoo's user base of more than 400 million in the browser and anti-virus sectors, said a company report released by Hong Kong-based Guosen Securities.

"We expect Qihoo to gain some market share from Baidu that may at least enhance its revenue by 30 percent within three years," the report said.

But some analysts argued that it was too early to tell if Qihoo can beat Baidu. "The dramatic change in market share does not reflect a shift in advertising revenue," said Dong, from Analysys International.