Police on Friday said they had arrested two men on suspicion of inciting others to commit arson and attack or kill police officers and government officials.
Officers said the pair, aged 22 and 34, are also accused of urging people to join unauthorised assemblies after Sunday's Legco polls, and of calling on people to adopt various means to influence the elections.
The force claimed that one of the two men is the administrator of a 2,000-member online forum where people allegedly posted messages inciting others to commit illegal acts.
Superintendent Tam Wai-shun, from the cyber security and technology crime bureau, said officers seized an imitation firearm, a combat helmet, a tactical vest and a gas mask from the home of one of the two suspects.
He also warned that it is illegal for people to incite others not to vote, or to cast blank ballots, in an election.