Hong Kong pro-democracy protesters defied a ban against gathering at a park to commemorate today's anniversary of China's deadly Tiananmen crackdown, with tensions rising in the financial hub over a planned new security law.

The city had for three decades seen huge vigils to remember those killed when China's communist leaders deployed its military into Beijing's Tiananmen Square to crush a student-led movement for democratic reforms.

This year's vigil was banned, with authorities citing coronavirus restrictions on group gatherings. 

But pro-democracy campaigners in Hong Kong, who have been waging a long struggle against what they see as China's tightening grip on the city, were determined to make their voices heard.

Hundreds of people, including some prominent democracy leaders, broke through barriers at Victoria Park where the vigil is held each year just as night fell.

"I've come here for the vigil for 30 years in memory of the victims of the June 4 crackdown, but this year it is more significant to me," a 74-year-old man said inside the park.

"Because Hong Kong is experiencing the same kind of repression from the same regime, just like what happened in Beijing."

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Some of the people in the park wore black t-shirts with the word "Truth" emblazoned in white. Others shouted pro-democracy slogans including: "Stand with Hong Kong".

Police maintained a presence near the park but did not move to disperse the protesters.

The defiant gathering came hours after Hong Kong's passed a bill criminalising insults to China's national anthem.

Beijing has been infuriated by Hong Kongers - especially football fans - booing the national anthem to signal dissatisfaction with China's rule. 

The new law, which needs to be signed by Hong Kong leader Carrie Lam, criminalises insults to the national anthem with up to three years in jail and fines. 

The city's pro-democracy opposition say the bill is a fresh attempt to criminalise dissent and fights have broken out between rival politicians over the legislation. 

The vote was delayed after politician threw a jar of foul-smelling fertiliser in the legislative chamber to protest China's refusal to acknowledge the Tiananmen crackdown. 

The debate was later moved to a different room and the bill was swiftly passed. 

China's communist rulers forbid discussion on the mainland of the Tiananmen crackdown, during which hundreds - by some estimates more than 1,000 - people were killed.

Hong Kong had been the only part of China where such mass displays of remembrance were possible.

On the campus of Hong Kong University, students spent the afternoon cleaning a memorial to the Tiananmen dead known as "The Pillar of Shame".

The city was engulfed by seven straight months of huge and often violent pro-democracy protests last year -- rallies that kicked off five days after the last annual vigil.

In response to those demonstrations last month Beijing announced plans to impose the security law, which would cover secession, subversion of state power, terrorism and foreign interference.

China says the law - which will bypass Hong Kong's legislature - is needed to tackle "terrorism" and "separatism" in a restless city it now regards as a direct national security threat.

Opponents, including many Western nations, fear it will bring mainland-style political oppression to a business hub.

But in mainland China, the Tiananmen massacre is greeted by an information blackout, with censors scrubbing mentions of protests and dissidents often visited by police ahead of 4 June.

Students write messages on footpaths in Hong Kong to mark the anniversary of the massacre

The United States and Taiwan have issued statements calling on China to atone for the deadly crackdown. 

"Around the world, there are 365 days in a year. Yet in China, one of those days is purposely forgotten each year," Taiwan's President Tsai Ing-wen tweeted. 

Secretary of State Mike Pompeo tweeted a photo of him meeting prominent Tiananmen survivors as US racial justice protests continue. 

Yesterday, China's foreign ministry described calls for Beijing to apologise for the crackdown as "complete nonsense".

"The great achievements since the founding of new China over the past 70 or so years fully demonstrates that the developmental path China has chosen is completely correct," spokesman Zhao Lijian told reporters.