Thousands of royalists thronged to Bangkok's Grand Palace Sunday for a glimpse of the Thai king, a massive show of support after months of protests calling for an overhaul of the government and reform of the monarchy.

King Maha Vajiralongkorn sits at the apex of Thai power, his influence permeating every aspect of society.

The king and queen greet supporters as they leave the palace
The king and queen greet supporters as they leave the palace AFP / Jack TAYLOR

But the once-unassailable institution faces unprecedented challenges from a growing pro-democracy movement, some of whose leaders call for reforms including an end to draconian royal defamation laws.

On Sunday, royal devotion was on display as thousands wearing yellow shirts -- the royal colour -- waited near the Grand Palace clutching portraits of King Vajiralongkorn and Queen Suthida.

Thailand's monarchy faces unprecedented challenges from a growing pro-democracy movement
Thailand's monarchy faces unprecedented challenges from a growing pro-democracy movement AFP / Lillian SUWANRUMPHA

"We will live loyally, die faithfully," chanted the crowd as he emerged from the palace to greet them. "Long live the King!"

Zigzagging through the crowd, the inscrutable monarch received flowers from his supporters, at one point saying "thank you" and signing his portrait, according to footage from local media.

The monarchists were dressed in yellow, the royal colur
The monarchists were dressed in yellow, the royal colur AFP / Jack TAYLOR

The king -- who spends long periods of time in Germany -- has been in the kingdom in recent weeks to mark a Buddhist holiday and the anniversary of his father's death.

The visit has coincided with non-stop demonstrations from mostly young activists, who have staged guerilla rallies drawing thousands to Bangkok's most traffic-clogged intersections as a show of defiance.

While the movement is leaderless, they are united in their demand for the removal of Premier Prayut Chan-O-Cha, a former military chief who came to power after staging a coup in 2014.

A royalist supporter holds a portrait of Thailand's King Maha Vajiralongkorn
A royalist supporter holds a portrait of Thailand's King Maha Vajiralongkorn AFP / Jack TAYLOR

But calls for reform of the monarchy have drawn a backlash from Thailand's conservative bloc, rousing royalist groups to stage their own rallies.

"We came here to show our loyalty to the king," said Bin Bunleurit, a Thai former actor who decried the students' demands.

Controversially, the students have also called for a clear accounting of the palace's finances -- which the extremely wealthy king took control of in 2018 -- and for the monarch to "stay out" of politics.

"It is not reform, it is about overthrowing the monarchy," Bin insisted to reporters outside the palace.

So far, pro-democracy protests have remained peaceful, but scores of students and activists have been arrested and charged -- some with the serious crime of sedition.

Over the weekend three high-profile student leaders were released on bail, only to be swiftly accosted as authorities attempted to re-arrest them on another charge.

A scuffle with plainclothes police landed them in hospital.

On Sunday night one of the trio, Parit "Penguin" Chiwarak, pledged in a Facebook post that they would keep pushing for their goals.

"If the people do not step back, we will not step back," he wrote.