The night of July 23, 2011, the area around the city of Wenzhou was drenched by thunderstorms. At around 8:30 p.m., bright light suddenly tore apart the darkness—not more lightning, but an enormous crash—one high speed train colliding into the rear of another. Together, these two trains were carrying more than 1,500 passengers. Several cars derailed and plunged off the viaduct, hitting the ground; one was left dangling over the bridge. At least 40 people were killed in the accident, and hundreds more were injured.

Going simply by casualties, the July 23 train collision was not the most horrific accident in China’s recent history, but its social impact was enormous, thanks to China’s burgeoning social media, especially weibo, or microblog. Less than 24 hours after the collision, the number of weibo posts about the accident carried by Sina, the biggest weibo operator in China, surpassed three million. Sina Weibo helped transform the occasion into a public crusade against the negligence, arrogance and dishonesty of the Chinese government, while highlighting one of China’s fundamental social conflicts: the country’s relentless pursuit of economic growth at the price of common people’s wellbeing.

For that, the July 23 Wenzhou train collision might go down in history not as an accident, but as a defining moment of weibo’s power. Foreign social media services, including Twitter and Facebook, are banned in China. China’s weibo services, originally an imitation of Twitter, first emerged in 2007. Adopting Twitter’s standard, each post on weibo cannot exceed 140 Chinese characters, which actually accounts for considerably more content than the same number of English alphabet letters—140 Chinese characters is equivalent to roughly 70 words.

What turned weibo into a national sensation was the launch of Sina Weibo in 2009, a service provided by China’s most influential web service and content provider, sina.com.cn. Within two years, Sina Weibo gained 300 million registered users, and the number has since been growing fast. Scholars use weibo to propagate their ideas, celebrities use it to connect with their fans, common folks use it to share moments of life, etc., etc. But they all use weibo, in one way or another, to criticize the authorities.

A Chinese TV journalist, for example, once investigated evidence of misconduct by a powerful real estate developer but was ordered to keep his findings off the air, so he posted the gist of the story on weibo. It was reposted dozens of times before the reporter deleted it at the request of a supervisor. He told me he at least felt some comfort that the public was not kept completely in the dark.

Indeed, like all mass media in China, weibo is subject to intense scrutiny of online censors known as the cybercops. Just how pervasive and effective are the cybercops? I once tested it myself.

On June 4, the anniversary of the 1989 pro-democratic demonstration in Tiananmen Square, I posted on weibo, from Kansas, the news of the death of Chen Xitong, who was the mayor of Beijing in 1989 and was seen as one of the top officials who supported the troops’ firing at the demonstrators.  Within minutes, this post had more than 3000 views and was retweeted 34 times. About 15 minutes after I posted the news, I got a message from Sina Weibo telling me this post had been “encrypted,” meaning it could no longer be seen. In the spot of the post, a message read, “This post is not appropriate for public viewing and is blocked.”

But for me, 15 minutes is enough for getting the information out, and it is better than having no voice at all. That is why weibo is still vastly popular and powerful despite tight online censorship. For millions of weibo users, “to watch is a power,” a phrase referring to public attention on weibo. Every time someone reposts or comments on a weibo post, this generates more material in the public arena, and the public attention alone puts pressure on the authorities.

As long as the Chinese government does not formally ban weibo services, weibo will continue to function as a public forum for disseminating and discussing public issues of a broad range, including current news, providing a venue for opinions and information not available on traditional media. And hopefully, it will continue to facilitate social change.

Josie Liu is an assistant professor in the communication department.