BANGKOK -- Thousands of demonstrators defied police warnings and occupied a historic field in Thailand's capital on Saturday to support the demands of a student-led protest movement for new elections and reform of the monarchy.

A fiery late-night speech with harsh criticisms of the royal institution set the crowd abuzz, even though the country has a harsh law that mandates a three- to 15-year prison term for defaming the monarchy.

The speaker, Arnon Nampha, is a lawyer who broke the taboo on criticism of the monarchy ahead of the pack at a small rally in early August with some mild questions about the institution.

He recalled Saturday night how the crowd went silent on that occasion, and compared its reaction to the much more enthusiastic reception he was now receiving for significantly more strident remarks.

The protesters, whose rally was continuing past midnight, have more activities planned for Sunday. They have been purposely vague about a planned march, but Arnon revealed in his speech that the protesters would lay down a plaque dedicated to the power of the people.

The action appear to be an implicit reference to the mysterious disappearance in 2017 of another decades-old bronze plaque that commemorated the 1932 revolution that turned Thailand -- then known as Siam -- from an absolute monarchy into a constitutional monarchy.

The crowd at Sanam Luang, a large field that has seen many historic events, were a disparate batch. An LGBTQ contingent waved their iconic rainbow banners, while red flags sprouted across the area, representing Thailand's Red Shirt political movement, which battled the country's military in Bangkok's streets 10 years ago.

Organizers had predicted that as many as 50,000 people would take part in the weekend's protest. Estimates of attendance at mass political events in Thailand are notoriously unreliable, but Saturday's crowd appeared as big as any protest held at that venue in the past three decades. Associated Press reporters estimated that around 20,000 people were present by early evening, while people were still arriving.

As the night progressed, there were skits, music and speakers on the stage. They touched on issues including the alleged incompetence of the government, corruption in the military and women's rights.

The Grand Palace complex, a famous tourist destination whose golden highlights are dramatically lit at night, shined behind the side of the field opposite from the stage.

"The people who came here today came here peacefully and are really calling for democracy," said Panupong Jadnok, one of the protest leaders.

At least 8,000 police officers reportedly were deployed for the event, which attracted the usual scores of food and souvenir vendors.

The core demands declared by the protesters in July were the dissolution of parliament with fresh elections, a new constitution and an end to intimidation of political activists. They have held a series of rallies since then.

They believe that Prime Minister Prayuth Chan-ocha, who as then-army commander led a 2014 coup toppling an elected government, was returned to power unfairly in last year's general election because the laws had been changed to favour a pro-military party. A constitution promulgated under military rule is likewise undemocratic, they charge.

The activists raised the stakes dramatically at an Aug. 10 rally by issuing a 10-point manifesto calling for reforming the monarchy. Their demands seek to limit the king's powers, establish tighter controls on palace finances and allow open discussion of the monarchy. Their boldness was virtually unprecedented, as the monarchy is considered sacrosanct in Thailand.

The students are too young to have been caught up in the sometimes violent partisan political battles that roiled Thailand a decade ago, Kevin Hewison, a University of North Carolina professor emeritus and a veteran Thai studies scholar, said in an email interview.

"This is why they look and act differently and why they are so confounding for the regime," Hewison said. "What the regime and its supporters see is relatively well-off kids turned against them and this confounds them."

The appearance of the Red Shirts, besides boosting the protesters' numbers, links the new movement to the political battling that Thailand endured for a large part of the past two decades. The Red Shirts were a movement of mostly poor rural Thais who supported populist billionaire Prime Minister Thaksin Shinawatra after the army ousted him in a 2006 coup. Thaksin was opposed by the country's traditional royalist establishment,

The sometimes violent subsequent struggle between Thaksin's supporters and foes left Thai society polarized. Thaksin, who now lives in exile overseas, noted on Twitter on Saturday that it was the anniversary of his fall from power and posed the rhetorical question of how the nation had fared since then.

"If we had a good government, a democratic government, our politics, our education and our healthcare system would be better than this," said protester Amorn Panurang. "This is our dream. And we hope that our dream would come true."

Arrests for earlier actions on charges including sedition have failed to faze the young activists. They had been denied permission to enter the Thammasat University campus and Sanam Luang on Saturday, but when they pushed, the authorities retreated, even though police warned them that they were breaking the law.

Students launched the protest movement in February with rallies at universities around the country in reaction to a court ruling that dissolved the popular Future Forward Party and banned its leaders from political activity for 10 years.

The party won the third-most seats in last year's general election with an anti-establishment stance that attracted younger voters, and it is widely seen as being targeted for its popularity and for being critical of the government and the military.

Public protests were suspended in March when Thailand had its first major outbreak of the coronavirus and the government declared a state of emergency to cope with the crisis.

Royalists have expressed shock at the students' talk about the monarchy, but actual blowback so far has been minor, with only halfhearted organizing efforts by mostly older royalists.