Protesters had wanted to gather in Causeway Bay to call for international aid to support the months-long social movement in the city, reports the South China Morning Post.
But before the event even began tensions flared outside the park with officers pepper-spraying one man and arresting him.
Police also conducted body searches on those wearing masks and fired tear gas to disperse a crowd on Hennessy Road.
The illegal rally, alongside three authorised ones in Central and Tsim Sha Tsui, marks the 22nd straight weekend of anti-government protests in Hong Kong.
At least three rounds of tear gas were fired soon inside Victoria Park, where protesters had gathered in defiance of a police ban against an anti-government rally.
Meanwhile, pro-democracy candidates for this month's district elections were pushed back into Victoria Park by police.
The candidates earlier said they would hold meetings with small numbers of voters in a bid to try and get around the ban on public assemblies at the park.
The Hong Kong protests, which have been drawing massive crowds since June following a contentious proposed extradition law, have mutated into a movement that seeks to improve the democratic mechanisms that govern Hong Kong and safeguard - or expand - the region's partial autonomy from Beijing.
However, some demonstrators have opted for more radical tactics than peaceful civil disobedience and violent clashes with the police have been frequent.
( With inputs from IANS )