By Krassimira Twigg
YouTube and several blog-hosting websites are permanently blocked
On the eve of the 20th anniversary of the Tiananmen killings, social networking sites such as Twitter and the photo-sharing site Flickr were blocked in China in an attempt by the government to prevent online discussion on the subject.
But Chinese twitterers proved that there are ways to get round the great firewall of China.
Frequent twittering from users in China has contributed to Tiananmen becoming one of Twitter's most discussed topics during the anniversary.
One twitterer wrote: "I cried when I watched a video about 4 June 1989. All my memory came back. We are living inside a big wall, like in prison."
Another one recalled the events of 1989: "I was fifth grade at school that year. There were students gathering in the town square. I could feel that there was a different atmosphere in our small town, but I couldn't understand why. It wasn't until I went to university that I learned about what had happened."
Those who are not old enough to have personal memories of 1989 forwarded link to articles in foreign media or simply re-tweeted other people's posts.
Links to photos of plain-clothes policemen blocking the lenses of foreign journalists with their umbrellas was a popular tweet.
Many tweets on unrelated topics carried the subject (hashtag) Tiananmen. As one user pointed out, people typed Tiananmen on every single post, so the topic is within the 10 most popular ones on Twitter.
Besides the Tiananmen anniversary itself, what seemed to be most important to Chinese twitterers was the blocking of sites. Advice on how to access Twitter - by using a proxy, VPN (virtual private network) or Hotspot shield - spread around quickly.
While some were clearly annoyed at this interference, others did not lose their sense of humour. One user congratulated his fellow twitterers with "Happy Chinese Internet Maintenance Day!".
While Twitter got blocked, Facebook remained accessible. There, fans of Tank Man [the man who stood in front of the tanks in the iconic photograph of the protests] were free to remember those who took part and the victims of the crackdown.
The Tank Man has attracted nearly 3,000 fans on Facebook
Shanghai resident Jim Chang from the Facebook fan site Tank Man is not sure how successful China's attempts to censor the web really are.
"It only slows down the search and it's just another hassle I have to live with. There are too many alternatives on the internet. If one site is blocked, it's annoying, but we move on to another."
The slow internet speed is not the only concern. A businessman from Beijing, who prefers to remain anonymous, points out that the blocking of sites limits the flow of not only political, but other ideas too.
"Entrepreneurs and technical experts too need to exchange ideas with their peers on social networking sites," he said.
For example, because blogspot is blocked, one of my business blogs is not accessible in China. This is not helping China become a technology innovator. While the world evolves into information society, China blocks the information flow."
"The blockade completely defeats its purpose. Many young people already know about Tiananmen and they don't care. But they do care about things happening to them, close to their lives, like unsafe food, corruption and unfair legal cases. They need a place to talk about these things and they get angry when sites are blocked."
The firewall affects education too, according to another internet user. A student from Shanghai, who also prefers to remain anonymous, says that the blocking of websites makes it very hard to do research.
"Twitter is my main source of news and information. I usually read about things that the government doesn't care about, like technology, yet I am still facing problems," he says.
"Everyone assumed that Twitter would be unblocked after the Tiananmen anniversary, but I guess the authorities noticed the large number of tweets on the Tiananmen anniversary and decided to block it for longer."
A law graduate from Jiangsu, who contacted the BBC News website, is doubtful whether the blocking of sites can fool people for much longer.
"Those websites give us the opportunity to get different ideas, which can influence the way we think. I call this a mind revolution. I am certain that Chinese people won't be so easily fooled anymore, which will make our government's job a lot tougher and will eventually bring about democracy in China."