Authorities in December placed bounties on six pro-democracy figures based abroad for allegedly violating the Chinese city's national security laws -- a move criticised by the United States as "transnational repression".

Deputy police commissioner Andrew Kan said police had looked into the Hong Kong-based associates of bounty targets, adding it was normal to collect intelligence from people with links to wanted fugitives.

"We brought in their family and friends to assist our investigation," Kan told reporters on Tuesday.

The aunt and uncle of London-based activist Carmen Lau were taken from their Hong Kong home on Monday morning and were seen leaving a police station hours later.

"The national security apparatus has now extended its reach to my extended family... This is nothing more than an attempt to intimidate Hong Kongers," Lau said on social media platform X.

National security police confirmed to AFP on six separate occasions since January 13 that it had "brought individuals to police stations" to help with investigations.

At least 10 people -- including the wife, son, three siblings and three ex-colleagues of former pollster Chung Kim-wah -- were questioned during that period.

Most of them left police stations within hours and no arrests have been made.

None of them have publicly commented on their situation. Under the national security law, people who "assist with the handling of a case" must follow confidentiality rules.

- 'Targeting friends and family' -

Political dissent in Hong Kong was effectively quashed by a sweeping national security law imposed by Beijing in 2020 after huge, sometimes violent protests the year before.

Authorities have placed bounties on a total of 19 overseas democracy advocates since 2023, while scores of opposition figures have been arrested and jailed in Hong Kong.

The bounties are seen as largely symbolic given that they are for people living in nations unlikely to extradite political activists to Hong Kong or China.

The US-based Hong Kong Democracy Council said the latest developments showed how China is "significantly expanding the scope of its well-worn tactic of targeting friends and family of dissidents".

Lau and Chung both said they have cut ties with former associates still based in Hong Kong.

Chung was an executive at one of Hong Kong's last independent polling bodies, the Hong Kong Public Opinion Research Institute (HKPORI).

Aside from government popularity ratings, HKPORI also conducted polls on Hong Kongers' political identity and views on the 1989 Tiananmen Square crackdown -- a sensitive issue in Hong Kong and mainland China.

Hong Kong security chief Chris Tang told AFP in January that the move to question Chung's ex-colleagues had "absolutely nothing to do with the results of (the group's polls)".

HKPORI said days later that it had suspended all self-financed research activities "due to various technical reasons".