A pro-democracy Hong Kong radio host went on trial Thursday for sedition in the first use of the colonial-era law since the city's handover to China as authorities broaden their criminalisation of dissent.

Tam Tak-chi, 48, is among a growing number of activists charged with sedition, a little-used decades-old law that prosecutors have dusted off in the last twelve months.

It is separate from the sweeping national security law that was imposed on Hong Kong last year, which has also been used to prosecute dissidents.

Best known by his moniker "Fast Beat", online talk show host Tam faces eight sedition charges for slogans he either uttered or wrote between January and July last year.

He also faces other charges including inciting an unlawful assembly and disorderly conduct.

At the opening of his trial on Thursday, prosecutors read out those slogans, as well as some pro-democracy speeches Tam gave, often littered with colourful Cantonese curse words.

The slogans included "Liberate Hong Kong, revolution of our times", "Corrupt cops, all of your family go to hell", "Disband Hong Kong police, delay no more" and "Down with the Communist Party of China".

The trial is a watershed legal moment for Hong Kong because it will set a precedent for what political phrases and views are now deemed illegal as China looks to stamp out dissent following huge and often violent democracy protests two years ago.

Hong Kong DJ Tam Tak-chi, better known as 'Fast Beat', is facing trial for sedition under a colonial-era law
Hong Kong DJ Tam Tak-chi, better known as 'Fast Beat', is facing trial for sedition under a colonial-era law AFP / ISAAC LAWRENCE

On Tuesday, a Hong Kong court convicted a former waiter of terrorism and inciting secession in the first trial conducted under the new national security law.

During that trial, judges ruled that the popular protest slogan "Liberate Hong Kong, revolution of our times" was secessionist and therefore a national security crime.

Tam's trial was delayed so judges could wait for Tuesday's verdict, which was from a higher court.

In Hong Kong, sedition is broadly defined as any words that generate "hatred, contempt or disaffection" towards the government or "encourage disaffection" among residents.

It was first penned by colonial ruler Britain in 1938 and had long been criticised as an anti-free speech law.

By the time of Hong Kong's 1997 handover, it had not been used for decades and was a largely forgotten relic on the statute books in a city that had become a regional bastion of free speech.

But China is currently remoulding Hong Kong in its own authoritarian image and the newly created national security police unit has resurrected the sedition law.

Last week, five members of a pro-democracy Hong Kong union that published children's books about sheep trying to hold back wolves from their village were arrested for sedition.

Three have since been charged and remanded into custody.

Sedition carries up to two years in jail for a first offence.

In contrast, the national security law is much harsher with up to life in prison for those who are convicted of serious offences.