HONG KONG — A jittery Hong Kong was again engulfed by clashes between protesters and the police on Sunday, hours after tens of thousands of people marched in a largely peaceful show of force against a contentious ban on face masks.

Two large marches on Sunday afternoon were the first significant public gatherings since the ban took effect the day before, under a rarely invoked emergency powers law. Despite pouring rain, angry protesters turned out en masse, many on edge from the growing violence of the recent weeks and from patriotic celebrations around a politically important Chinese anniversary this past week.

The large marches and the widespread defiance of the ban were symbols of the staying power of the monthslong pro-democracy movement, and a test of the local government’s resolve and ability to stop its momentum.