Facebook may be eyeing a move into mainland China, but web firms there cast doubt on whether the social networking giant can tap the monster market -- assuming authorities lift a ban on the site.

China has the world's biggest internet population, with 420 million users and rising. It is a hugely lucrative landscape, but is also peppered with dominant domestic brands, technical hurdles and the threat of censorship.

Beijing has set up a vast online censorship system sometimes dubbed the "Great Firewall of China" that aggressively blocks sites and snuffs out Internet content on topics considered sensitive.

The system currently prevents most of the nation's web users from accessing Facebook. The key role the website played in anti-government protests in Egypt and Tunisia will not have gone unnoticed by China's communist rulers.

But Facebook last week said it had opened a Hong Kong office, its third in Asia, while founder Mark Zuckerberg visited China in December, prompting suggestions that Beijing may eventually welcome the California company.

Blake Chandlee, Facebook's vice-president and commercial director for emerging markets, played down any imminent move into the country.

"We have no plans right now to talk about entering into mainland China and trying to be aggressive in that," he told AFP at Hong Kong Social Media Week, which wrapped up Friday.

Still, Facebook already has an estimated 14 million Chinese-language users -- mainly based in Taiwan, Singapore and Hong Kong -- and the figure is expected to keep growing.

But even if Facebook got clearance for a China foray, some observers said it would have trouble adapting to local tastes.

"China is a different market," said Jeffery Zheng, general manager of renren.com, a popular social networking site in China.

"A lot of companies like Yahoo! and Google tried unsuccessfully to penetrate the Chinese market. You have to satisfy local needs."

Last year, search engine Google claimed it was the victim of a sophisticated cyber attack in 2009 that originated from China, apparently aiming to gain access to email accounts of Chinese human rights activists.

Google shut down its Chinese search engine, automatically re-routing mainland users to its uncensored site in Hong Kong, but later ended the automatic redirect to avoid having its Chinese licence suspended.

Zheng said his firm had notched up 170 million registered users by the end of 2010, a 400 percent increase from 2008, because of "unique" services such as letting customers choose their own wallpaper, background music and Chinese New Year-themed emoticons.

"Chinese netizens love to share their emotions indirectly... This is reflected in their profuse use of emoticons," he added of the yellow "smiley" symbol.

"The Internet has become a way for them to communicate in a relaxed way."

Meg Lee, general manager of the Hong Kong version of Sina.com, a Chinese microblogging service similar to Twitter, said her firm has enabled Chinese users to blog by text messaging from their mobile phones.

"In China, people send a lot of SMS to family and friends," she said.

"We provide a unique service in synchronising their SMS messages to their blogs. This is very popular as many people are still using basic mobile phones."

Lee warned that any newcomer to the China market -- where Twitter is also banned -- would have to wrestle with the country's strict censorship policies, although some regulations have been gradually relaxed.

"Every environment has game rules. Censorship is the policy in China that everyone has to follow," she told AFP.

Added Zheng from renren.com: "I know that the government pays special attention to us because we are a social networking site so we might be considered to be stirring up trouble.

"If a blogger writes strong words against the government on our site, of course we will take it out."

Still, many Chinese web users are relatively unconcerned about government censors -- as long as they get their daily dose of entertainment gossip.

"Many people just want to follow movie stars and idols," Lee said.

In fact, the biggest hurdle for Facebook and other firms may be China's less-than-dependable Internet infrastructure and reams of bureaucratic red tape, said Li Lei, head of online start-up Wincasting.

"It is necessary to get approval from many different governmental departments," Lei said.