“We are most worried about gatherings, or people using this occasion to drum up [tensions],” one source said, adding the force was also concerned about radical individuals launching “lone-wolf” attacks.

Asked if solo activities such as walking alone with a candle would be discouraged, the source said officers would evaluate the public impact of those actions.

“It depends on the actual situation – whether that person appears at a certain location or time, or what they intend to do. Would their presence trigger others?” the source said, explaining that while the individual action might “seem fine”, it could become problematic if others around were influenced or affected.

Chen, the artist, was also taken away by police in the same district and on the same day last year, after he was heard chanting, “Do not forget June 4! Don’t be afraid of them, Hongkongers!”

The force’s counterterrorism response unit, police tactical unit and an anti-riot “Sabre-toothed Tiger” vehicle were deployed along with uniformed patrol officers, as well as plain-clothes police.

The source also said there were concerns about possible “antagonistic disputes” near a food fair held at Victoria Park by some pro-Beijing groups.

By 7pm on Monday, more than 30 uniformed officers were seen on Great George Street opposite Sogo department store in Causeway Bay.

Four plain-clothes officers were seen standing outside Exit F of Causeway Bay MTR station.

At the park itself, six officers stood guard at the Gloucester Road entrance, while 13 others were spotted patrolling inside.

Two others monitored junctions near the Gloucester Road entrance and between Great George Street and Paterson Street. At 8.20pm, the “Sabre-toothed Tiger” vehicle was parked outside Sogo.

A spokesman for the force later said officers patrolling near Lockhart Road took a man to a police station for investigation after he caused a commotion in the area. He was later released.

Police banned the annual candlelight vigil in 2020 on public health grounds during the Covid-19 pandemic.

Police said the 62-year-old man was arrested in Sha Tin on suspicion of committing offences with seditious intent, which came on the back of the first arrests made last week under the Safeguarding National Security Ordinance.

A source confirmed the man was a maternal uncle of activist Chow Hang-tung. Chow and her mother, Medina Chow Lau, were also arrested last week.

Monday’s arrest coincided with the release of an advisory notice from education authorities telling schools to teach pupils about how the new legislation protected the city.

They should also educate youngsters about the Safeguarding National Security Ordinance passed in March, and arrange for lessons to take place on school days to mark the fourth anniversary of the first, Beijing-imposed, national security legislation.

“This can be done during morning assemblies, class teacher periods [and] talks in the school hall,” the circular said.

Teachers were told they should remind pupils to report suspected cases of endangering national security to police and emphasise the law’s positive aspects, such as how it protected the city and the country.

“Of course, if we discover something that endangers the country, we can report it to relevant units such as the National Security Department’s reporting hotline to fulfil our citizen responsibilities,” the advisory said.

“As the saying goes, ‘national security is everyone’s responsibility’.”

Additional reporting by Olga Wong