China is casting an increasingly wary eye over the Internet and its 50 million bloggers amid a year of sensitive anniversaries and job losses that could trigger unrest, analysts and rights groups said.

Amnesty International said this week its website had been blocked in China, and the BBC's Chinese language Internet page was shut down in December, after both sites were re-opened during last year's Olympic Games.

China's communist authorities have also recently shut down sensitive domestic websites such as bullog.cn, an influential liberal blog platform, as well as fatianxia.com, where many legal scholars aired their opinions.

Meanwhile, a high-profile crackdown on pornographic websites was launched this month -- a drive that analysts said had previously taken place alongside a clampdown on politically sensitive Internet sites.

"2009 is a year with lots of sensitive anniversaries and then the economic downturn on top of that is really affecting China," said David Bandurski, a researcher for the China Media Project at the University of Hong Kong.

"Controlling the media continues to be a top priority for the (Communist) Party... but there has been a shift towards the Internet as a focus."

China's censors have long regarded the Internet as a major threat to their efforts to control the flow of information, and this problem grows daily as more and more Chinese go online.

Official data released this week showed China's Internet population had risen to 298 million in 2008, a stunning 42 percent rise from 2007.

Meanwhile, the number of bloggers in China surpassed 50 million.

Amid this backdrop, Amnesty said it was concerned about a broader online crackdown in 2009.

"Our fear is that this is signalling the beginning... (of) something that's going to last through what one might call the sensitive year," Amnesty Asia Pacific deputy programme director Roseann Rife said of recent website closures.

This year marks the 20th anniversary of the Tiananmen Square pro-democracy protests that were brutally put down on June 4 by the army, and 50 years since an uprising in Tibet in March led to the Dalai Lama's flight into exile.

The 60th anniversary of the founding of the communist republic also falls on October 1, 2009.

Despite the so-called "Great Firewall of China," the Internet has allowed many people to voice dissent and find others who have similar grievances.

"The Internet has become a very effective way to mobilise disgruntled groups, and the government is aware of that," said Zheng Yongnian, a professor at the National University of Singapore's East Asian Institute.

Online discontent has recently led to demonstrations in China, according to Xiao Qiang, director of the China Internet Project at the University of California at Berkeley.

As one example, Xiao pointed to taxi strikes in southern China last year that were triggered by online and mobile phone communication.

But Xiao said the sheer number of bloggers and netizens in China made it extremely hard for the government to exert control.

"Individual bloggers say a few things... but aggregating them together is making a bigger public opinion," he said.

"That is something the Chinese government is really battling."

Analysts also pointed to well educated graduates who might be unable to find jobs this year as a potential new area of concern for the country's leadership.

"This is a more educated, web-savvy section of the population that could use these tools to express their grievances," said Bandurski.

But Xiao said there was still a big difference between online expression and offline coordination of protests in China.

"There is more and more of a potential but overall that is still a very tightly controlled area," he said.