China's Communist authorities ban their own people from accessing major global social media sites including Facebook, Twitter, YouTube and more. But when it comes to self-promotion they are increasingly keen users themselves.

The official news agency Xinhua, the Communist Party's official mouthpiece the People's Daily, and state broadcaster CCTV all have Twitter accounts, as do a host of city and provincial authorities.

When the city of Hangzhou, renowned for its lakes and canals, looked to raise its international profile it turned to Facebook, the world's most-popular social network.

China's Internet users, who now number 618 million, have been blocked from using it since 2009.

But the city's "Modern Marco Polo" competition -- akin to Australia's "best job in the world" contests -- involves no fewer than six Facebook apps.

The winner, to be announced Tuesday, will receive 40,000 euros ($55,000) and a two-week trip to Hangzhou, in exchange for promoting the city on Facebook and Twitter for a year.

Michael Cavanaugh, a consultant for British-based PR Agency One, which has been promoting the contest, told AFP increasing official use of such sites was "inevitable". But he declined to say how the winner was expected to post to them from within China.

- Great Firewall of China -

China's Communist authorities maintain a tight grip on expression -- both on- and off-line -- fearful of any dissent that could spiral into a challenge to one-party rule.

Some Chinese Internet users and businesses use VPNs, or virtual private networks, to bypass the vast censorship apparatus known as the Great Firewall, and state-run media often use foreign bureaux to accomplish the same goal.

Hangzhou itself used a digital agency in Hong Kong, where Facebook is not blocked, to administer its contest -- an increasing trend by cities and provinces within China's borders.

The social media giant is actively seeking business in the country.

"We want to help tourism agencies in China tell the rest of the world about the fabulous things in China that are really not that well-understood," Vaughan Smith, Facebook's vice president of corporate development, told a Beijing audience last month.

Facebook is reportedly in talks to open a sales office in the Chinese capital, and in recent weeks the company has quietly posted Beijing-based job openings on its website, including one for a client solutions manager to "focus on planning, implementing, and optimising advertising campaign spending for the world's top-tier advertisers".

Its executives are making increasingly frequent appearances at high-profile events in China, and the company's chief operating officer Sheryl Sandberg drew international headlines last September when she met the head of China's State Council Information Office, which oversees propaganda efforts.

Google also seeks advertisers in China and has three offices on the mainland, but pulled out its servers in 2010 in a row about censorship.

Twitter, which is a prominent advocate for free speech online, has shown few signs of interest in setting up in China, although the company's CEO Dick Costolo met Shanghai government officials during his first China visit in March.

Facebook representatives declined interview requests about the company's China business.

Duncan Clark, chairman of Beijing-based tech consultancy BDA, said Chinese local authorities had huge budgets and their tourism advertisements were probably lucrative for the multi-billion-dollar firm.

However, Facebook was unlikely to see them as a way of gaining access to Chinese users, Clark said.

"There's kind of a common-sense, logical middle ground where Facebook and China will agree to trade with each other," he told AFP. "This is business sense. I wouldn't expect that to change."

- Netizens: 'discriminatory' -

Other promotions include the "Rebirth of the Terracotta Warrior" Facebook contest launched last month by Shaanxi province, home to the tomb of China's first emperor Qin Shihuang.

A "Chengdu Pambassador" campaign gave contestants a chance to become a "guest panda keeper" at the southwestern city's giant panda base through a series of Facebook activities.

But critics of Chinese censorship say such schemes give Beijing a soft-power boost through sleight-of-hand.

A co-founder of anti-censorship website GreatFire.org who uses the pseudonym Charlie Smith told AFP: "I think the average Western netizen doesn't put two and two together and realise actually, these websites are blocked in China.

"That helps China, for sure, because it gives this impression that Facebook is actually open and free for the people who don't know that it isn't," he added.

The double standards have not escaped the notice of Chinese web users.

The Shaanxi provincial government announced the opening of its tourist board's Facebook, YouTube and Twitter accounts in a posting on Weibo -- a Chinese version of Twitter -- in February.

Several users angrily responded that they were unable to open the links, the Southern Metropolis Daily reported.

"We're not advocating that domestic tourists visit these pages," a provincial government representative told the paper, drawing even greater fury.

"This way of thinking is discriminatory against Chinese people," wrote one online commentator. "It shows a lack of understanding of the basic rules of tourism promotion. It's very stupid and quite laughable."