HONG KONG—Thousands of protesters besieged the city’s police headquarters on Friday, extending a political crisis in the city sparked by a proposed extradition law that the government has since put a stop to in an effort to ease unrest.

Demonstrators—many young and including students—chanted Friday at police to take responsibility for the use of tear gas and projectiles to disperse demonstrators during one of a series of streetprotests last week.

The...