Hong Kong's oldest university covered up one of the last public tributes to the deadly 1989 Tiananmen Square crackdown on Saturday, as Beijing continues to muzzle dissent in the financial hub.

Hong Kong was the only place in China where mass remembrance of Tiananmen was tolerated, but authorities have driven such activities underground after imposing a sweeping national security law on the city.

The University of Hong Kong (HKU) last month removed a famous statue commemorating pro-democracy protesters killed by Chinese troops around Tiananmen Square.

At least two other local universities removed artworks in public areas marking the crackdown that same week.

Hong Kong's oldest university has covered up one of the last public tributes to the deadly 1989 Tiananmen Square crackdown Hong Kong's oldest university has covered up one of the last public tributes to the deadly 1989 Tiananmen Square crackdown Photo: AFP / Bertha WANG

On Saturday, a large slogan painted on an HKU campus bridge mourning the Tiananmen "martyrs" that had escaped the earlier censorship was blocked with metal sheets.

An AFP reporter saw construction workers covering the calligraphy, which read: "The heroic spirit of martyrs slaughtered in cold blood will live forever, the fire of democracy that overcomes evil will never be put out".

Created by HKU students shortly after the crackdown, it had adorned the campus for more than three decades according to local media.

The calligraphy birthed a campus ritual with students leaders annually repainting the words in white to symbolise mourning.

Created by HKU students shortly after the crackdown, the calligraphy birthed a campus ritual with students leaders annually repainting the words in white to symbolise mourning Created by HKU students shortly after the crackdown, the calligraphy birthed a campus ritual with students leaders annually repainting the words in white to symbolise mourning Photo: AFP / Bertha WANG

HKU did not immediately respond to AFP's questions on whether the words will be permanently erased.

But a spokesperson told reporters that the university "regularly conducts maintenance works at various locations and facilities, with the above site being one such project".

Hong Kong's universities, ranked among the best in Asia, had long been free of the political censorship that pervades mainland campuses.

But Beijing has begun remoulding Hong Kong in its own image following huge and often violent democracy protests in 2019.

The national security law has effectively criminalised dissent including commemorating Tiananmen with authorities stressing the need for schools to foster "patriotism".

An annual candlelight vigil to mark the June 4 crackdown has been banned for the past two years, with officials citing both security and pandemic fears.

Leaders of the now-disbanded group organising the vigil have been charged with subversion, and authorities have shut down a Tiananmen museum formerly run by the group.

After dismantling the "Pillar of Shame" Tiananmen statue last month, HKU said the decision was "based on external legal advice and risk assessment for the best interest of the University".