HONG KONG — China hosts some 300 million microblog accounts (includingmy own), and officials say that domestic social media put out more than 200 million posts every day. In hopes of getting a handle on this potentially threatening surge of information, the government has started a campaign that aims to quash what it calls “rumors” — statements that it says threaten the public order but that it has not bothered to define. After a series of public opinion disasters this past year, the Communist Party has been pressuring social media providers to weed out allegations it finds threatening, and state media have tried to whip up fear over their malignant social effects.

The party’s fever over rumors began in August, following the July 23 high-speed rail collision in Wenzhou. The government took a public opinion beating over the crash, in large part because social media harnessed anger over the bungled rescue effort, the safety of the high-speed rail network and corruption in the Railways Ministry. Once party leaders wrested back control of the story, they pushed all relevant facts into the darkness, leaving only rumors to sate the public’s appetite for the truth. Likewise, even though both the Guo Meimei affair, which exposed corruption at the government-run Red Cross Society of China, and the well-organized public demonstrations against a chemical project in Dalian were true enough, they were never reported outside the “rumor-mill” of Chinese social media.

And then bowing to government pressure, in August social media companies like Sina Weibo, China’s most popular microblog platform, began sending users notices of posts that they claimed were rumors. One of the first notices to flitter across my computer screen announced that another user’s account had been suspended for a post alleging that a murder suspect in Wuhan had been released on bail thanks to his well-connected father. Sina’s rumor-busting notice told users that the police in Wuhan had “confirmed” that “the suspect was still in custody.” End of discussion. “Is this real or fake?” users posted in response. But the case was closed. And the upshot seemed to be that a rumor is what the government says it is, as a matter of political convenience.

The government’s mania has reached new rhetorical heights. At high-level meetings in October, the party decided to “strengthen the control and use of microblogs and other newly emerging media.” But even as it fears the consequences of more open speech, the government understands that actions to control it are deeply unpopular, especially on social media. And so now it is couching its antirumor policy by sugarcoating censorship as a kind of public health measure.

Stricter controls are the prescription for what China’s top Internet control official, Wang Chen, last week called a “healthy and upright online culture.” Get vaccinated, wash your hands, and don’t climb in bed with strangers. Xinhua warned us again on Nov. 28 that “like all forms of vice and iniquity, Internet rumors are extremely infectious” and are capable of “poisoning the social environment and impacting social order.” Once something has been marked as a social disease, it is simple enough to justify its elimination.

But rumors are not confirmed falsehoods; rather, they are unverified statements. The only way to prove them wrong is to create an environment in which information can be freely reported and debated. In other words, government censorship only feeds China’s rumor mill.

Hu Yong, a professor at Peking University and one of China’s leading experts on new media, argues that state controls on public opinion had “nurtured a rich soil for the transmission of rumor” while undermining the credibility of official information. Or as Cheng Yizhong, the founder of Guangzhou’s Southern Metropolitan Daily newspaper, put it in September — on his microblog account, as he could not elsewhere — censorship is a great evil. “Rumors are the penalty for lies,’’ he wrote. ” They are a rebellion of speech by the weak against power, a small ill hoping to overthrow a great evil.”