“Even in the daily life of students, Hong Kong people have to defend their right for freedom and democracy and still face a threat from Beijing,” Mr. Wong said of the effort.

On the other side, some students from mainland China said they are afraid to speak their minds, regardless of their opinions.

(Just over 40 percent of New York’s nearly 100,000 international students are from mainland China and less than one percent are from Hong Kong, according to data from the Institute of International Education.)

Livi, 27, a mainlander who asked to go by her nickname and omit her last name and school for security reasons, was so anxious about returning to New York that there were nights when she couldn’t sleep, she said. Imagining the prospect of having to confront people with different views was terrifying, she explained. What if she heard people saying negative things about China?

“Should I defend my country? Do I have the responsibility to do that? What would that make me feel, if I don’t?” Livi said. “It’s a very troubling thought for me.”

Livi said that she has had civil discourse with some Hong Kongers. She doesn’t agree with them — “I think the aspiration of democracy is noble, but the consequence is destructive or detrimental” — but she has enjoyed some “honest, heartfelt exchanges.”