The alliance told the Post it was concerned police would accuse those watching the live broadcast together of sharing a “common purpose” and arrest them for unauthorised assembly. The law defines a public procession as one organised for a common purpose which takes place in, to, or from a public place.

A senior police source told the Post that all officers in five regional response contingents drawn from the elite Police Tactical Unit, emergency units and other teams, would be expected to be on standby across the city for any potential chaos on Friday, though the force was still finalising its approach.

The squad was disbanded, with officers returning to regular duties, in the latter half of 2020 after the social unrest had waned.

If people still took part in an unauthorised assembly at the park on Friday evening despite the ban, the senior police source said they should be prepared for a strict response.

“A lenient approach on unauthorised assemblies is not expected, as our operations need to bring deterrent effects after courts handed down lengthy jail terms to protesters,” the source said.

Tiananmen crackdown: ban on vigil but Hongkongers make plans to mark June 4

On what would constitute a breach of those rules, qualify as disorder in a public place, what slogans would break the national security law, and what actions officers might take, the insider said it all depended on their behaviour, the contents and the actual circumstances.

“There is no definitive answer to these questions,” they said. “It all depends on the situation. Officers would collect relevant evidence for investigation and seek legal advice when necessary.”

Another source said traffic police would set up roadblocks near Victoria Park and officers from the tactical unit would carry out stop-and-search checks around the venue.

Although there was no intelligence to indicate any trouble, the second source said police had to “prepare for the worst in case of mass turnout to the venue”, and the large deployment of officers to ensure there was “sufficient manpower ready to deal with any sudden occurrence”.

He said it was appropriate to prepare for trouble regardless of whether there was relevant intelligence, adding: “Nobody wants to be caught unprepared”.

06:13

Thousands of Hongkongers defy ban and gather to mark Tiananmen anniversary

Thousands of Hongkongers defy ban and gather to mark Tiananmen anniversary

A third source said there would be an increased presence around the June 4 museum in Mong Kok, which the alliance originally planned to open so people could place floral tributes to those killed in the 1989 crackdown.

Explainer | What the Tiananmen Square crackdown on June 4, 1989 was about

The Leisure and Cultural Services Department earlier pointed to the coronavirus pandemic when it said the alliance’s application for the use of Victoria Park on June 4 would not be processed.

The mass gathering in Causeway Bay has been the only large-scale commemoration of the crackdown on Chinese soil. Police banned the vigil on health grounds for the first time last year, but an estimated 20,000 people turned out at Victoria Park.

Last month, Wong was jailed for 10 months after pleading guilty to knowingly taking part in an unauthorised assembly, an offence that carries a maximum sentence of five years in prison. Three district councillors were also sentenced for up to six months for their roles in the June 4 event.

When sentencing, Judge Stanley Chan Kwong-chi criticised the group for openly defying the law, saying it was clear their actions had been “deliberate and premeditated”, at a time when Hong Kong’s public order situation remained volatile in the aftermath of the 2019 protests.

Chan said the court could not underestimate the event’s potential risk factor, as emotions could have run high, and the unruly might have taken advantage of that to incite violence.

So far, the city’s national security police have arrested more than 100 people and prosecuted 57 of them since the legislation came into force on June 30 last year.