The clashes raised the prospect that the unrest might further escalate in the coming days, testing the limits of the territory’s already strained economy and the patience of the ruling Communist Party in China.

On a deeper level, the move has triggered concerns that the government would take further steps to erode the civil liberties that have long differentiated Hong Kong from the rest of China and helped turn the city into an international trade and finance powerhouse. The government hopes the ban will deter the protesters from resorting to violence, but to many it represents a turning point that could fundamentally change the city’s identity and would only inflame tensions more.

“How can we move on when there are such intense and deep-rooted divisions within our society?” said Wendy Ng, a 44-year-old part-time cooking instructor who was staying home on Saturday because the authorities had shut down the subway network. “The mask ban is making it worse, can’t they see?”

“If the government does not make further concessions,” she added, “it’s over for this city, both for us and for those government officials who think of themselves as all-powerful.”

The ban announced Friday targets the face masks that protesters use to conceal their identities, but Mrs. Lam could, if she deemed necessary later, use the emergency powers to impose a curfew or empower the police to search phones more easily without warrants, among other measures.