In what looked to be a possible first enactment of the new law, riot police pinned down and questioned youth in the streets still wearing facemasks.
Protesters gathered after a peaceful march through the city.
“I’m so angry,” one demonstrator said.
“When we wear the mask in the protest, I think that’s it’s a way to protect ourselves," another said.
Protests on Friday night became increasingly violenct, forcing subway stations to shut down, which the local news outlets described as “unprecedented.”
Fox News has not confirmed any arrests related to facemask-wearing protesters. Experts have expressed the complications associated with arresting thousands of people who wear them.
Instead, it is seen more broadly as a deterrent.
The penalty for wearing a facemask includes one year in jail.
So far, the movement has seen four months of unrest in Hong Kong.