Groups of officers in riot gear conducted stop-and-search operations along an expected marching route linking the prime shopping district of Causeway Bay with the administrative Admiralty district.
Late on Wednesday, police said they had arrested five people for inciting participation in illegal assemblies online.
Local newspaper South China Morning Post reported earlier this week about 6,000 officers would be deployed on a day of heightened alert, citing unnamed sources.
Anti-government protests, which often turned violent in 2019, have been smaller and fewer this year due to coronavirus restrictions on group gatherings and fears over a sweeping national security law imposed by Beijing on June 30.