Police in Hong Kong say they have arrested six people on suspicion of violating the new national security legislation by posting seditious messages on Facebook and inciting hatred toward authorities.

Local media are reporting that these are the first arrests under the legislation that took effect in March.

The six arrested on Tuesday include Chow Hang Tung. She is a former vice chairperson of a group that used to organize annual vigils to remember the victims of the Tiananmen Square crackdown on June 4, 1989.

The Facebook page in question features posts about past vigils.

Police say the suspects targeted an "upcoming sensitive date," apparently referring to the incident's anniversary.

They also argue that the posts aimed to provoke hatred toward the central and Hong Kong governments and to incite netizens to organize or participate in illegal activities.

The vigils on June 4 were last held in 2019, as the government cracked down on the commemoration in 2020 citing the coronavirus.

Authorities are on high alert ahead of the 35th anniversary of the incident.

Security Secretary Chris Tang urged citizens not to be incited to take part in illegal acts and those that endanger national security.