In November, Hong Kong expressed its support for the protests at the polls, overwhelmingly electing pro-democracy politicians to neighborhood offices. It was a stinging rebuke to Communist Party officials in China, and it ushered in the longest period of relative calm since the protests began.

Wednesday’s march was the second large-scale demonstration that the police had authorized since the election, and tens of thousands took to the streets, if not more. But hours after it began, the police rescinded their permission, citing an outbreak of violence and vandalism. Large numbers of people were still waiting to march at the event’s staging area when the police made the announcement.

The Civil Human Rights Front, which organized the march, called the police’s decision “absurd” and accused them of escalating tensions by firing tear gas at a crowd. It said in a statement that unless protesters’ demands were met, “Hong Kongers shall not back down, and peace shall not resume with ongoing police brutality.”

By nightfall, familiar scenes were playing out on the streets, as protesters built barricades, lit fires and squared off against the riot police. Several dozen people were rounded up by the police in the Causeway Bay area; witnesses said some of them had been bystanders. A pro-democracy lawmaker, Ted Hui, was pepper-sprayed directly in the face by a police officer, after the officer tore off Mr. Hui’s protective goggles.