As Facebook nears saturation levels in some Western countries, Asian users are helping drive the social-networking leader's march on the 1-billion-user milestone and beyond.

The Facebook-led social-networking phenomenon has profoundly impacted the region -- challenging conservative ideals, connecting diaspora communities and allowing users to circumvent authoritarian information controls.

That impact looks set to deepen as Asia's huge population flocks to Facebook, representing a vital growth market for CEO Mark Zuckerberg's Harvard dorm-room creation as it readies for this week's hotly anticipated IPO.

More than one in four of Facebook's estimated 900 million-plus users are in Asia -- India's 45 million community and Indonesia's 42 million rank third and fourth worldwide behind the United States and Brazil.

In the past half-year, new users have grown 20 percent in India, 65 percent in Japan and 56 percent in South Korea, according to social media tracking website socialbakers.com.

"For the Facebook platform itself, Asia is wildly important. But in terms of the future of the platform, it is even more important," said Tom Crampton, head of Asian social media for advertising giant Ogilvy & Mather.

Facebook has steamrolled rivals Friendster and MySpace in Asia, fueled by factors including the long-distance communication needs of the hundreds of millions of migrant labourers from India, Indonesia, the Philippines and elsewhere who work abroad in the region.

But social-networking sites have also enabled users to challenge social strictures and break information monopolies, forcing governments to take notice.

Discontent aired online in tightly controlled Singapore last year was a major factor in the ruling party's worst polls showing in its five decades in power.

In Malaysia, whose users on average have the most "friends" of any country, according to a 2010 survey by a global research firm, Facebook and other platforms were used to pump up turnout for pro-democracy protests by tens of thousands last month, and to criticise a tough police response.

Meanwhile, premier Najib Razak has repealed some authoritarian laws in a campaign widely seen at winning over the increasingly vocal online population.

Asian governments and corporations are being forced to listen and respond, said Yasir Yousuff, managing director of NM Incite, the social media arm of market research firm Nielsen.

"(Singapore and Malaysia showed) Facebook and social media have played a huge part in providing a platform for people to voice their feelings and create symbolic actions that can help rally people to the cause," he said.

In China, Facebook and other Western social media are blocked by Communist authorities but have inspired Chinese clones that -- while heavily censored -- have been used to channel public pressure on the government.

Conservative Asian mores also have been challenged in countries such as Muslim Indonesia, where Facebook is a popular way to find romantic partners across the nation of 17,000 islands, angering religious authorities.

"Asians are not as aggressive at networking in person as an American or European might be. Facebook has really tapped into that psyche that you can easily form groups of like-minded people," said Napoleon Biggs, head of digital media for Asia at marketing firm Fleishman Hillard.

Challenges remain for Facebook in Asia.

Besides China, India's potential is crimped by poor infrastructure and low Internet penetration while domestic Japanese and South Korean rivals pose stiff competition in those markets.

But rich potential remains, according to Nielsen.

It said in a recent report that consumers in developing Asian markets like Thailand, the Philippines, Vietnam and Indonesia spend far more time online than their developed-country counterparts for everything from watching video content to researching purchasing decisions.

For Facebook, the future in Asia will depend heavily on its ability to capitalise on the region's famed affinity for the mobile phone, analysts said.

Friendster was tops in Indonesia -- where mobile Web access dominates -- until Facebook's application for Blackberry took off in the past few years.

"Almost overnight, it went from being a Friendster nation to a Facebook nation. Mobile is a great untapped revenue source for Facebook in Asia," Crampton said.