The Yuen Long attack, and the police's apparent failure to prevent it, exacerbated tensions during protests last year, plunging the global financial hub into crisis.
Fueling the scramble, Britain, Australia, Canada, the United States and Taiwan have all proposed measures to help accommodate Hong Kongers.
"I’m scared of going to jail but for justice I have to come out today, I have to stand up," said one 35-year-old man who gave his name as Seth.
The new operation likewise focused heavily on protests in Hong Kong, but also promoted messages about the coronavirus pandemic, exiled Chinese billionaire Guo Wengui and Taiwan, the researchers said.
It was the first time there had been unrest during the annual Tiananmen vigil in Hong Kong, which police had prohibited this year citing the coronavirus crisis.
Justice minister Teresa Cheng said the basis for Trump's actions was "completely false and wrong," saying the need for national security laws were legal and necessary.
Pressed if this would include sanctions, he said: "No it's something you're going to be hearing about ... before the end of the week, very powerfully I think."
The arrests on Saturday were the biggest crackdown on the city's pro-democracy movement since the outbreak of mass protests last year.
"They are doing whatever they can to try to silence, to take down, the local opposition."