Beijing revamped Hong Kong's electoral system in 2021 to ensure that only "patriots" could hold office, and the December 7 poll will select a second batch of lawmakers under those rules.

Fewer than a quarter of the seats are directly elected.

Authorities charged a 68-year-old retiree with the national security crime of "seditious publication", saying he had repeatedly published posts online that provoked hatred towards the government and incited others not to vote.

Offenders face up to seven years in prison.

Three others, two men and a woman aged between 55 and 61, were charged with reposting content inciting others not to vote, which carries a maximum penalty of three years in jail and a fine of HK$200,000 ($25,700).

Authorities issued arrest warrants for two more people outside the city who were alleged to be the authors of the posts.

Hong Kong made it a crime in 2021 to tell others not to vote or to spoil their ballots, even though voting is not mandatory.

Its top court will hear a legal challenge in May on whether the criminal offence infringes on constitutional rights such as the freedom of expression, according to Hong Kong media.

The Beijing-imposed overhaul of Hong Kong's electoral setup came after months of huge and sometimes violent pro-democracy protests in 2019.

The first legislative race held under the new system in December 2021, which featured no pro-democracy candidates, drew a record low turnout of 30 percent.

Authorities have blanketed much of the city in promotional material this time, with Hong Kong leader John Lee urging the public last month to fulfil their "civic responsibility".

Trains will extend services on election day, while some businesses have promised to give employees a half-day off if they head to the polls.