This was seen clearly after two high-speed trains collided in July last year near Wenzhou, a city close to Shanghai. Much of the information about the incident, which claimed 40 lives, spread on Weibo and there was little the authorities could do to control it.
Such unofficial information dissemination, and the use of the Weibo sites by those keen to express views on politics, means the authorities are "very concerned" about the medium, according to Jeremy Goldkorn, the founder of Danwei, a Beijing media website and research company.
"Weibo is the most powerful tool for public expression China has ever had. It's a very real force that's changing public debate," he said.
The authorities try to restrict discussion, insisting on real-name registration and deleting controversial material or preventing it from being posted in the first place.
Users who breach rules, by spreading rumours for example, now risk having their accounts deactivated. Yet the sites remains a potent medium, allowing views to spread.
"It's certainly a force that's pushing China toward a more pluralistic environment in terms of the public expression of opinions and debates," said Mr Goldkorn.
Yet as well as allowing more diverse opinions to be aired, online discussion can also magnify hardline views.
In particular, extreme nationalism can dominate discussions when there are disputes with other countries, such as the recent spat between Beijing and Manila over the South China Sea.
"There was a lot of very angry nationalism on Weibo," Mr Goldkorn said. This is a potential concern given that a 2010 report, New Foreign Policy Actors in China, published by the Stockholm International Peace Research Institute, warned nationalism was "a dangerous tool" that could harm the government if it is not tough enough with foreign countries.More in The National.
Jeremy Goldkorn is a speaker at the China Speakers Bureau. Do you need him at your meeting or conference? Do get in touch or fill in our speakers' request form.