Hong Kong is not becoming a "police state", the city's top law enforcement officer said Tuesday, days after his officers stamped out the city's once-permitted commemorations marking Beijing's deadly Tiananmen crackdown.

The Chinese business hub is preparing for an upcoming leadership change as well as the 25th anniversary of the city's handover from Britain, for which President Xi Jinping is widely expected to visit.

Speaking to local outlet HK01 about beefed-up security activity around the event, commissioner Raymond Siu Chak-yee rejected criticism that the police were becoming too powerful.

"A police state is where the government forcibly controls various aspects of people's life with administrative measures and without going through legal procedures. Do people think Hong Kong is like that?" he said.

"Hong Kong is a society of rule of law, not a police state."

His comments come after police arrested six people on Saturday as authorities pounced on any attempt to publicly remember China's 1989 crackdown on peaceful protesters.

Amnesty International has accused authorities of "harassment and indiscriminate targeting" for the arrests.

Police closed the site of a once annual Tiananmen vigil and jampacked the surrounding area, one of the busiest shopping districts in Hong Kong, with officers.

People were stopped and searched for carrying flowers, wearing black and, in one case, carrying a toy tank box.

On Tuesday authorities rolled out a "counter-terrorism reporting hotline" for residents to report "violent acts, suspected terrorism-related activities, in particular extremist plots".

Police closed the site of a once annual Tiananmen vigil and jampacked the surrounding area with officers
Police closed the site of a once annual Tiananmen vigil and jampacked the surrounding area with officers AFP / Peter PARKS

People would be paid for "reliable" information, they said.

Since Beijing imposed a national security law on Hong Kong in 2020 after large and sometimes violent pro-democracy demonstrations, authorities have cracked down on dissent.

In another interview with the South China Morning Post, Siu "advised" residents they should not watch or download an award-winning documentary about the 2019 protests if they are uncertain about the legal risk.

The film, "Revolution of Our Times", has recently become widely available on US streaming platform Vimeo.

Siu did not however specify whether the movie or the production team had violated any law or had been investigated by the force's national security unit.

"If they're not sure whether this would commit [offences under] the national security law, then I would advise them to try to distance themselves from doing such acts," Siu told the Post.

Produced by Hong Kong director Kiwi Chow, the movie takes its name from a then popular -- but now outlawed -- protest slogan.

It debuted at the Cannes film festival last July and in November won best documentary award at Taiwan's Golden Horse Award, an event dubbed the Chinese-language "Oscars".

It has never been shown commercially in Hong Kong as the city toughened film censorship after the passage of the security law, and Chow sold the rights to his work overseas to avoid scrutiny.