The 24-year-old received the new sentence on Thursday for taking part in an unsanctioned protest last year to mark the anniversary of China's bloody crackdown on the democracy movement on June 4, 1989, Hong Kong media reported.

Three district councillors sentenced alongside him received between four and six months of jail time.

The annual candlelight vigil was banned last year for the first time due to pandemic-related restrictions, but some 20,000 people gathered anyway.

The judge argued there was a potential risk of violence because of the crowd and that it was therefore necessary to use this punishment to deter others from committing similar offences, broadcaster RTHK reported.

Wong, who is seen as the face of the pro-democracy movement in Hong Kong, is already jailed over his role in other 2019 protests.

He was supposed to be released in November.

The councillors Lester Shum, Tiffany Yuen Ka-wai and Jannelle Rosalynne Leung are also in custody on charges of violating Hong Kong's security law. They were denied release on bail.

Beijing enacted a sweeping new national security law in Hong Kong on June 30 last year.

The law targets subversion, secession, terrorism and collusion with foreign forces, but is widely seen as a bid to crack down on dissent.

Hong Kong was handed from British to Chinese control in 1997 and it was agreed the territory would retain a level of autonomy and be governed independently under the "One Country, Two Systems" principle.

Australian Associated Press