A 6.4 meter (20 foot) tall bronze "Goddess of Democracy" statue holding aloft a flame at Hong Kong's Chinese University had been removed from a public piazza just before dawn.

The university said in a statement that the "unauthorized statue" had been taken away.

"Following an internal assessment, and as the manager of the university campus, CUHK has removed the statue," it read.

The Hong Kong sculpture was modelled on a 10-metre (30 feet) white plaster and foam statue erected by students in Tiananmen Square in 1989 as a symbol of their resolve in pursuing liberty and democracy in China under Communist party rule.

"I feel heartbroken and shocked," said Felix Chow, a former Chinese University student and district councilor.

"This statue represents the school environment is open. It's a symbol of academic freedom ... It makes people doubt whether the school can still ensure the space is free and people can speak freely," he told Reuters.

Unlike mainland China, where Chinese authorities ban any memorials or public commemoration of June 4, Hong Kong had previously remained the only place on Chinese soil where such commemorations were permissible.

Hong Kong's Lingnan University also took down a Tiananmen massacre wall relief sculpture, that also included a depiction of the "Goddess of Democracy".

The bas-relief includes images of a line of tanks halting before a lone protester known as "tank man"; and victims shot by Chinese troops being carried away.

Pictures of the Lingnan site after the removal showed a bare wall and rubble on the ground.

The artist, Chen Weiming, who created both the statue and wall relief, told Reuters that he would sue the universities if there was any damage to his works.

A towering red picture of the Goddess of Democracy in the Lingnan University student union main hall had also been painted over in grey paint. Students responded by pasting a sheet of paper with the word "shameful" on the effaced image, that was quickly ripped off by security guards.

Lingnan University said in an email to Reuters that items that may pose "legal and safety risks" had been "cleared or removed and stored appropriately".

Hong Kong returned from British to Chinese rule in 1997 and was promised wide ranging autonomy and freedoms by China under a so-called "one country, two systems" arrangement.

Authorities have been clamping down in Hong Kong under a China-imposed national security law that human rights activists say is being used to suppress civil society, jail democracy campaigners and curb basic freedoms.

Chinese and Hong Kong authorities say the security laws have restored order and stability after mass protests in 2019, and that fundamental rights and freedoms are still respected.

Earlier this week, the University of Hong Kong dismantled and removed an eight-meter tall "pillar of shame" statue from its campus site that for more than two decades has commemorated pro-democracy protesters killed during China's Tiananmen Square crackdown in 1989.

The disappearances of these symbolic monuments at three universities in quick succession mean there are now hardly any remaining public Tiananmen memorials in the financial hub.

"Since the Chinese communists implemented the national security law in Hong Kong, they have eradicated the freedom of press, of assembly and the freedom of expression," Chen, the artist, told Reuters.

"They want to remove the real history of the brutal crackdown ... they wouldn't allow any different viewpoints to continue to exist in Hong Kong."

When asked by Reuters whether Hong Kong or Chinese authorities had instructed all three universities to remove these Tiananmen monuments, the office of Hong Kong's leader, Carrie Lam, gave no immediate response.