HONG KONG — Four student union leaders at the University of Hong Kong were arrested on Wednesday on suspicion of “advocating terrorism” after they had held a moment of silence for a man who stabbed a police officer and then killed himself.

The arrests, by the new national security police in Hong Kong, represented the latest crackdown on opposing voices as the Chinese territory tries to snuff out any sign of the dissent that flared during the 2019 protest movement.

University students were among the most determined and vocal protesters during the pro-democracy demonstrations in the city in recent years. And Hong Kong officials have used a national security law imposed on the city by Beijing last year to target campuses, which they have branded as dangerous incubators of antigovernment sentiment.

Wednesday’s arrests stemmed from a live-streamed meeting on July 7, when the student union held the moment of silence and passed a motion expressing “deep sadness” over the man’s death and appreciation for his “sacrifice.”

cancer cells” that were endangering the city. The ranks of student activists have diminished under pressure from university administrators and government officials. Many have said they are fighting for survival against the Chinese Communist Party’s tightening grip.

“To tell the truth, it feels like we’re just waiting to die,” Yanny Chan, a union leader at Lingnan University, said this year.