The protesters, many wearing masks, marched beyond the official end-point of the rally, which took place on Sunday, to make their way toward the office, close to the heart of the financial center.
Some protesters pelted eggs at and spray-painted anti-government graffiti on the walls of the office building.
Hundreds of riot police took up positions close to the office in order to prevent incidents during the rally, which had proceeded peacefully along the police-mandated route. Law enforcement forces also used blue and white water-filled barriers to barricade government and police headquarters during the rally. The march focused on calls for the full withdrawal of an extradition bill that the government of the semi-autonomous Chinese region has already declared “dead.”
At a separate rally on Sunday night, police fired tear gas to clear crowds of protesters who had taken over streets in the heart of the city.
Hong Kong has been the scene of violent protests for weeks over the proposed amendment to the city’s extradition law. The protesters now also demand Hong Kong Chief Executive Carrie Lam’s resignation.
The latest protests come a day after tens of thousands gathered to voice support for security forces.
On Friday, police seized explosives and weapons in an industrial building in the New Territories district of Tsuen Wan.
Hong Kong, a former British colony, was returned to China in 1997 under a “one country, two systems” deal that guarantees it a level of autonomy, including a separate and independent legal system.
Beijing has warned against foreign interference as well as violence by the protesters.