Candidates banned from standing for election in Hong Kong because they are advocating a split from mainland China have led a pro-independence rally in the city as tension over the upcoming vote escalates.

Key points: Five pro-independence candidates rejected by election officials led the rally

Five pro-independence candidates rejected by election officials led the rally Thousands of protesters and activists gathered in support

Thousands of protesters and activists gathered in support Independence is dismissed as illegal by Beijing and HK authorities

Five pro-independence candidates who tried to register were rejected by election officials who said their stance went against Hong Kong's mini-constitution.

Critics have slammed the move as censorship as fears grow over Beijing interference in the semi-autonomous city in a range of areas, from politics to media and education.

A park near the government's harbour-front headquarters filled with thousands of supporters of all ages through Friday evening.

Most sat calmly on the grass, many of them holding "Hong Kong Independence" placards and flags, as they listened to activists speak.

They applauded as banned candidate Edward Leung, the leader of new party Hong Kong Indigenous who is gaining a growing following, addressed the crowds.

"Hong Kong's sovereignty does not belong to [Chinese President] Xi Jinping, does not belong to the authorities, and does not belong to the Hong Kong government. It belongs to the Hong Kong people," Mr Leung said.

Protester Satomi Cheng, a 49-year-old office manager, said many in the city were angry about China's tightening grip.

"Day by day our human rights ... are taken away by the Hong Kong government and the Chinese government," she told reporters.

'Hope for the best, prepare for the worst': Joshua Wong

Some acknowledged that independence was a pipe dream in the face of a powerful Beijing, but said the city was running out of options.

"China has destroyed Hong Kong politics ... we are supporting freedom and democracy," said student Clayton Chow, 19.

Andy Chan, 25, leader of the pro-independence Hong Kong National Party and a disqualified candidate, said the rally was a chance to talk about the future.

Sorry, this video has expired Leading activist Joshua Wong says he is seeking self-determination from China.

Pro-independence activists including Mr Chan have previously advocated violence — he said they had now decided that would not work.

"We don't want people to get hurt or arrested, so we want to start with a public meeting and hopefully it will be a healthy path for us to get stronger," he said.

The idea of independence is dismissed as illegal by Beijing and Hong Kong authorities, and was a taboo subject until recent months, when new parties emerged campaigning for a breakaway.

Demosisto, a new party set up by Umbrella Movement activists including well-known campaigner Joshua Wong, has made self-determination its central platform, although it does not cast itself as a localist organisation.

Wong, who was recently found guilty of unlawful assembly related to the 2014 protests and faces up to five years in jail, told the ABC's The World program that he is "hoping for the best, but preparing for the worst".

Those calling for self-determination have been allowed to stand in September's legislative vote.

AFP/ABC