Public activities in Hong Kong come with security risks and only last month there was an attempt to hijack a women's rights march that was eventually called off, Secretary for Security Chris Tang warned on Monday.

Tang was responding to comments by two former members of the now-defunct Confederation of Trade Unions that authorities should protect rights guaranteed under the Basic Law and not "exaggerate" such risks. The pair, Joe Wong and Denny To, are waiting to see if they will get police approval to hold a march on May 1, marking Labour Day.

The security chief said it is irresponsible for people to play down the security risks associated with public activities.

"Our risk assessment is completely based on facts and past events... we all witnessed the black violence in 2019 where some people hijacked public events," he told reporters at the airport ahead of a trip to the mainland.

"On March 5th this year, during the originally planned march about women’s rights, there was an attempted hijack. Therefore, the organisers acted responsibly and cancelled the event. I want to say these safety risks do exist."

Tang said while the police can ensure that events are held in a safe environment, organisers also have a responsibility to make sure activities pass off peacefully.

"It is your responsibility to take reasonable actions which you are capable of doing to ensure that these activities are not interfered with or hijacked, which includes identifying official participants and preventing the event from being hijacked," he said.

The minister said he will discuss issues such as national security, cross-border crimes and the exchange of talent in his meetings with officials in Beijing, Guangzhou and Shenzhen this week.