How Tiananmen Square vigils in Hong Kong have become unlawful

Chow Hang-tung is on trial for inciting subversion but says what is truly on trial is Hong Kong law. (ABC News)

Closing arguments have been heard in the trial of Hong Kong pro-democracy activists who organised a vigil to commemorate the 1989 Tiananmen Square massacre.

Advocates say the trial is part of a crackdown by Beijing on long-enjoyed freedoms in Hong Kong.

Lee Cheuk-yan and Chow Hang-tung face up to 10 years in jail if convicted of "incitement to subversion".

A lone man faces down a line of tanks: known only as 'Tank Man', his bravery during the Tiananmen Square massacre has been remembered at vigils in Hong Kong for decades.

That is until Beijing cracked down on events held on June 4, the anniversary of the massacre.

China has worked hard to erase the defining image of the Tiananmen Square massacre. Thirty years after the uprising, we asked Beijing students what they know about 'tank man'.

Earlier this month, Hong Kong's High Court began hearing closing arguments in the case of two democracy activists, Lee Cheuk-yan and Chow Hang-tung, charged with inciting subversion for organising a candlelight vigil to remember Tiananmen Square.

Experts warn it's a sign of China's increasingly hardline stance and are concerned that the world is forgetting about human rights in Hong Kong.

On June 4, 1989, months of pro-democracy and freedom protests came to a head in Tiananmen Square, Beijing.

Under leader Deng Xiaoping, the Chinese Communist Party (CCP) ordered an estimated 180,000 troops and police to enter with tanks and armoured vehicles.

Using live ammunition, soldiers forced their way through crowds.

Over seven weeks in 1989, students led peaceful pro-democracy protests centred on Beijing's Tiananmen Square. (AP: Sadayuki Mikami)

Estimates range from hundreds to thousands of people killed.

Nearly 40 years later, the reverberations from that event are still being felt, as the Chinese government continues to stifle mention of the massacre and has cracked down on people in Hong Kong who attended events to remember it.

The photo of a man in front of a convoy of tanks became the defining image of the Tiananmen Square massacre. (Reuters)

Lee and Chow, two former leaders of the Hong Kong Alliance in Support of Patriotic Democratic Movements of China, have pleaded not guilty to "incitement to subversion" after organising vigils on the massacre anniversary.

A third defendant, 74-year-old Albert Ho, a former lawyer, pleaded guilty in January.

When the British handed back Hong Kong to China in 1997, Beijing promised that the "capitalist system and