Chinese protesters have turned to blank sheets of paper to express their anger over Covid-19 restrictions in a rare, widespread outpouring of public dissent that has gone beyond social media to some of China’s streets and top universities.

Images and videos circulated online showed students at universities in cities including Nanjing and Beijing holding up blank sheets of paper in silent protest, a tactic used in part to evade censorship or arrest.

The latest wave of anger was triggered by an apartment fire that killed 10 people on Thursday in Urumqi, where some people had been locked down for as long as 100 days, fueling speculation that Covid lockdown measures may have impeded residents’ escape.

In Shanghai, a crowd that started gathering late on Saturday to hold a candlelight vigil for the Urumqi victims held up blank sheets of paper, according to witnesses and videos. One widely shared video said to be from Saturday, which could not be independently verified, showed a lone woman standing on the steps of the Communication University of China in the eastern city of Nanjing with a piece of paper before an unidentified man walks into the scene and snatches it away.

Other images showed dozens of other people subsequently taking to the university’s steps with blank sheets of paper illuminated against the night sky by flashlights from their mobile phones. A man could later be seen chiding the crowd for their protest.

“One day you’ll pay for everything you did today,” he said, in videos seen by Reuters. “The state will also have to pay the price for what it has done,” people in the crowd shouted back. Similar sheets of paper could be seen held by people gathering on the grounds of Beijing’s prestigious Tsinghua University to sing the Chinese national anthem on Sunday.

Protesters were advised to bring a sheet of white paper to at least one planned demonstration, according to tips being shared in chat groups seen by Reuters. Several Internet users showed solidarity by posting blank white squares or photos of themselves holding blank sheets of paper on their WeChat timelines or on Weibo.

By Sunday morning, the hashtag “white paper exercise” was blocked on Weibo, prompting users to lament the censorship. “If you fear a blank sheet of paper, you are weak inside,” one Weibo user posted.