Thousands of democracy activists marched on Thailand’s police headquarters (HQ) in Bangkok on November 18, defacing the compound walls with brightly coloured paint, a day after chaotic protests left more than 50 injured.

The kingdom has been rocked by months of protests demanding constitutional reform, the removal of Prime Minister Prayut Chan-o-cha and even changes to the untouchable monarchy.

Protesters – numbering some 20,000 according to an AFP estimate – packed a major intersection in the heart of Bangkok’s shopping and commercial district, after their leaders vowed to step up the movement.

After daubing anti-royal slogans on walls and the road, they marched on the heavily-defended national police HQ – led by a clown and a parade of giant inflatable rubber ducks.

They were accompanied by a Buddhist monk giving the three-fingered salute borrowed from the Hunger Games movies that has become emblematic of the youth-led protest movement.

Some protesters threw glass bottles and paint bombs over the walls of police HQ, which was barricaded with dumper trucks, concrete blocks and razor wire.

Others hurled paint at the outside walls, leaving them plastered with bright yellows and blues, while others used water pistols to squirt paint into the compound.

Fearing trouble, many protesters came equipped with helmets, goggles and gas masks, but after the impromptu paint job, they dispersed peacefully around 8:30pm (1330 GMT).

Prominent protest leader Jatupat Boonpattarasaksa called a new rally on November 25 outside the Crown Property Bureau, which manages the hugely wealthy monarchy’s estates.

November 18’s protest came a day after the most violent confrontations since the movement began in July, as police used tear gas and irritant-laced water cannon on protesters trying to reach parliament, and democracy activists clashed with royalists.

More than 50 people were injured, six of them with gunshot wounds, according to medical officials, though it is not clear who was responsible for the shooting.

‘Keep fighting’

Prime Minister Prayut has urged protesters to refrain from violence, but ruled out introducing another emergency decree – like the one banning public gatherings of more than four people which spanned a week last month.

But there is little sign the demonstrators are prepared to back down.

“We should not be afraid – this is just a transitional moment in our history,” Sirapop Poompuengpoot, another student leader, told the crowd on November 18.

“People are working for us in parliament and the rest is up to us – keep fighting.”

Police say they did not fire either live rounds or rubber bullets on November 17, and they are investigating who was behind the shootings of six people, which happened about 300m from the main protest zone near parliament.

The Thai Human Rights Lawyers Association slammed police tactics, saying they were “not in accordance with international procedure to disperse demonstrations”.

In New York, the UN called for authorities to exercise restraint.

“It’s very important that the government of Thailand refrain from the use of force and ensure the full protection of all people in Thailand who are exercising a fundamental peaceful right to protest,” UN spokesman Stephane Dujarric said.