UN rights chief "Volker Turk calls for these sentences to be quashed and reiterates his call for the National Security Law to be brought in line with China's international human rights law obligations", his office said in a statement.

A Hong Kong court on Friday sentenced Lee Cheuk-yan, 69, Albert Ho, 74, and Chow Hang-tung, 41, to between five and seven years behind bars for national security crimes, following a trial that has drawn international condemnation.

The United Nations, rights groups and foreign governments have condemned their convictions under a national security law that Beijing imposed on Hong Kong in 2020, following huge pro-democracy protests.

"Today's imposition of lengthy jail terms on three activists and a heavy fine on the affiliated civil society organisation is another regrettable outcome of the deeply flawed National Security Law," UN rights office spokesman Seif Magango said in Friday's statement.

The jailing of the three activists "shows the ever-increasing restrictions on civic space in Hong Kong, including harsh measures taken against civil society actors, since the law was passed", he charged.

Hong Kong and Macau were long the only places on Chinese soil that permitted public mourning for those killed on June 4, 1989, when Beijing sent troops and tanks to crush protests calling for political reform around the capital's Tiananmen Square.

But public commemoration has been effectively banned in the cities in recent years.

The trio were leaders of the now-defunct Hong Kong Alliance, the group that organised annual vigils in the city's Victoria Park.