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 they blamed for taking part in the earlier antigovernment protests, leaving 45 people injured.

Hong Kong Chief Executive Carrie Lam condemned the violence Monday as she was questioned by reporters about a breakdown in law and order following weeks of antigovernment protests.

“Hong Kong is an extremely safe city and having the rule of law has always been the most important part of society,” Mrs. Lam said.

But fears of new clashes in the city’s northern districts spread on social media, leading some businesses to close or send staff home early on Monday and fueling concern over the impact of the social turmoil on the economy.