Author Jin Song is relishing the challenge of beating China's army of censors and posting comments online about the country's impending leadership change, the first in the social media era.

Referring by name to the 18th Communist Party congress, set to begin next Thursday, can be difficult. One of Jin's posts on the subject was deleted and he received a message saying it had been removed by "system managers".

The trick is to find similar-sounding words in Chinese when writing on the heavily policed but hugely popular "weibo" sites such as Sina Weibo -- a microblog akin to Twitter, which is banned along with Facebook and YouTube.

Substituting homophones for political catchwords is second-nature to Chinese netizens, who poked fun at President Hu Jintao's call for social "harmony" by posting about "river crabs", a term that sounds similar to harmony in Chinese.

"If you want to post about top leaders or important government organisations, you need to write the characters differently," Jin told AFP. "I think of it as being like a game."

The 35-year-old, who has seen previous posts on environmental protests and official corruption beaten back by the censors' "Great Firewall of China", was not surprised by the clampdown. "The congress is a sensitive topic," he said.

In organising their secretive and highly choreographed power handover, China's communist leaders are for the first time having to contend with social networks that provide a platform for censorship-dodging debate and gossip.

China has witnessed explosive growth in Internet usage since the last Communist Party transition in 2002, with the online community of 538 million posing a huge challenge to the party's attempts to shape public opinion.

The country's microblogs have proved hard to keep in check, with fast-reacting weibo users increasingly challenging official accounts of news events.

Fierce online criticism of the government following a deadly rail crash in 2011 contrasted starkly with reports by state-run newspapers, which received orders to publish only "positive news" or information released by authorities.

In some cases, social media activism is tolerated and has even scored victories. Several local officials have been investigated and sometimes sacked after weibo users posted pictures of their luxury watches and multiple houses.

But anxious to protect the party's image and senior leaders, officials have pressured companies behind the websites to hire armies of professional censors, sometimes known as "secretaries" in Chinese.

Staying ahead of them is the key for those wanting to discuss events starting next week at the Communist Party congress when the party is expected to select Xi Jinping to succeed Hu as its new leader for the next decade.

In the run-up, Sina Weibo's website has received a patriotic makeover, with an image of Beijing's monumental Tiananmen square, the national flag and two white doves looming above users' posts.

But if any of its 368 million users searches for the most commonly used name for the meeting, which translates as "18 big", they are met with a blunt message: "Due to relevant laws, policies and regulations, the results of your search are not displayed."

Jeremy Goldkorn, founder of the website Danwei and an analyst of Chinese social media, told AFP that the list of censored words was "vast". They range from the sexual to the political.

When the New York Times reported last week that Premier Wen Jiabao's family held billions of dollars in assets, censors quickly deleted related posts and blocked searches for the names of Wen's family members.

"The idea that the senior leaders are incorruptible is a perception that the party likes to maintain," Goldkorn said.

"There's more room for criticism of everything on weibos, and that includes senior leaders, but the tolerance only goes so far," he said.

The relative openness of social networks contrasts with coverage in the state-run press.

Negotiations over top party positions during the congress are shrouded in secrecy, with little known about how leaders are selected. The media are kept out of most of the sessions.

China's newspapers are unlikely to alter their coverage of the congress, which will be dominated by official articles penned by state-run news agency Xinhua, according to David Bandurski, a researcher of Chinese media at the University of Hong Kong.

"It's a very controlled and very choreographed event," he said, with every newspaper likely to print "the exact same photograph of the new members of the (politburo) standing committee standing together stiffly".

"On the fringes, we'll see chatter and sarcasm about the party congress, and then we'll see it disappearing as (fast as) it appears," he added.

But Jin says he will continue to sneak posts past the censors, and sees weibos as the most open platform for news in China. "The authorities can't keep up with people's demand for information," he said.