HONG KONG — Police officers in Hong Kong on Saturday fired tear gas and clashed with protesters around the city, capping 21 weeks of antigovernment demonstrations that have convulsed this international financial hub and helped to sink it into a recession.

In scenes throughout the night that have become part of the new normal in Hong Kong, the city’s central financial district and several dense commercial neighborhoods were enveloped in shrouds of tear gas as riot police battled with protesters, who wore masks in defiance of a ban on face coverings enacted last month. Earlier in the afternoon, police shut down two rallies in the Central district that had received official authorization, citing the clashes elsewhere.

The day began when several thousand protesters turned out for a rally at Victoria Park in Causeway Bay. It had been billed as a campaign event for Hong Kong’s upcoming district council elections, after the police rejected the organizers’ initial application to hold a demonstration. (Police permission is not always required for election events.)