HONG KONG—Hong Kong police fired a barrage of tear-gas canisters at thousands of demonstrators late Sunday as public unrest stretched into a seventh weekend.

Antigovernment protesters came out in big numbers during the day and, as darkness fell, thousands began to occupy main thoroughfares and target official buildings. Several hundred demonstrators gathered outside the Chinese government’s liaison office, defacing the national emblem with black paint and pelting the building with eggs, before being driven back through key...