HONG KONG—Tech giant Apple Inc. shut its stores early citywide on Monday, as fears of escalating violence and spiraling lawlessness linked to weekslong protests spurred concern among businesses and the public.

A day after police fired tear gas in clashes with thousands of protesters, Hong Kong remains on edge as officials conceded no ground and activists accused the government of coddling a rise in vigilante justice. In the north of the city, a mob of white-shirted men stormed a subway station late Sunday and beat people whom...