Hong Kong police arrested six activists on Wednesday for suspected sedition and contravention of a national security law in connection with what the police called "causing nuisance" at court hearings in December and January.

Police, who typically do not identify arrested people, said the six were aged from 32 to 67, had been arrested for "having purposely caused nuisance" during various court hearings they attended.

They had been being detained for further investigation, police said.

Media said those arrested included Leo Tang, a former vice-chairman of the now disbanded Confederation of Trade Unions (HKCTU) and citizen journalist Siew Yun-long.

The six were accused of "affecting jurisdictional dignity and court operations" at the High Court, the West Kowloon Magistrates' Courts and the Eastern Magistrates' Courts, between December 2021 and January 2022.

Police raided their homes and seized "records of conspiracy to cause nuisance in the courts" as evidence.

The Hong Kong government did not immediately respond to a request for comment.

Reuters was not immediately able to contact Tang or Siew for comment.

The HKCTU was once the largest independent trade union in the former British colony, but was among dozens of groups forced to disband after Beijing imposed a sweeping national security law in 2020.

The law punishes crimes of secession, subversion, terrorism and collusion with foreign forces with up to life in prison, and has been criticised by Western governments as a tool to suppress dissent and curb freedoms.

Chinese authorities reject those assertions saying the law has brought stability to the financial hub after sometimes-violent mass pro-democracy protests in 2019.

Hong Kong returned to Chinese rule in 1997 under a "one country, two systems" formula, intended to guarantee its freedoms, including the right to protest and an independent judiciary.