Chung Kim-wah cheered Hong Kong’s return to China as a college student, before growing more critical of Beijing’s rule as an academic and pollster.

Now, his organization, the Hong Kong Public Opinion Research Institute, provides the type of independent surveys that are impossible on the mainland and frequently points out the deep unpopularity of top leaders, such as Chief Executive Carrie Lam. And lately, friends have been warning Chung to keep a lower profile as the city extends its crackdown on dissent from well-known activists to the nonprofit groups that have long helped push the government to consider opposition views.

"They are doing something to scare us, to threaten us and to indicate to us that we have to be careful,” said Chung, who is deputy CEO of the polling firm. "We’re trying to inform the society and inform the government. But if even this kind of scientific, impartial opinion polling is not allowed in Hong Kong, I think that would be a tragedy for Hong Kong, for the whole world and for China also.”