It was also the first major show of force since Prayut lifted Oct 15 emergency measures that had been meant to stop three months of protests against the government and monarchy, but which brought tens of thousands of people onto the streets.
"If he doesn't resign, then we must come out to ask him to quit in a peaceful way," protest leader Jatupat "Pai" Boonpattararaksa said as people chanted "Prayut Out".
The prime minister's office posted a note on Twitter to say he was not quitting. He has said the crisis should be discussed in parliament, which is due to hold a special session on Monday and Tuesday.
But his opponents have little faith in an assembly dominated by his supporters.
There was no sign of a major police presence around protesters at the Ratchaprasong Intersection, an emotive location for protesters as the scene of bloodshed in 2010 in a crackdown by security forces on anti-establishment protests.
A government spokesman said there would be no use of force and called on people to remain peaceful and respect the law.
In the relaxed atmosphere, a group of drag queens gathered to put on a show.
Protests since mid-July have put the greatest pressure in years on the establishment, particularly with taboo-breaking calls to limit the powers of King Maha Vajiralongkorn's monarchy.
On Monday (Oct 26), protesters are planning to march to the German Embassy in a message to the king, who is currently in Thailand, but spends much of his time in Germany.
"Going to the German Embassy reflects the evident problem of the king's exercise of power is making many people uncomfortable and raises questions whether it violates the German law," said activist Piyarat "Toto" Chongthep.
Protesters seek the departure of Prayuth and a new constitution. He rejects their accusation that he engineered last year's election to keep power he first took in a 2014 coup.
They have also demanded curbs on the monarchy, saying it has enabled decades of military domination.
AFP reported that - "Today is open for everyone who wants to talk about their dissatisfaction about Prayut's government," said Jatupat, who had called for the protest the night before.
He reaffirmed the movement's core three demands -- for Prayut to step down, a rewrite to the 2017 military-scripted constitution, and for authorities to "stop harassing" political opponents.
"If Prayut insists not to quit, we will keep insisting on coming out to oust him," Pai said.
The gathering saw a diverse crowd -- drag queens in full regalia, young people in hard hats ready for a police crackdown and older protesters worried about Thailand's freefalling economy.
"I want Prayut to think as a citizen rather than as a prime minister," said 43-year-old Nuch. "The economy is really bad -- since he cannot solve the problem, he should resign and let someone else do it."
Prayut remained resolute Saturday while attending a prayer ceremony for the country at a historic Bangkok temple, saying "all problems can be solved" through compromise.
He also told reporters he "won't quit".
The movement is largely leaderless though the different groups are united when it comes to their demands for an overhaul to Prayut's government.
Some are also issuing controversial calls for reform to the kingdom's unassailable monarchy, questioning the role of King Maha Vajiralongkorn in Thailand -- once a taboo act due to draconian royal defamation laws.
Another group called the People's Movement announced a march to the German Embassy on Monday afternoon -- in apparent defiance of the king, who spends long periods of time in Germany.
The monarch has been back in Thailand for the past week and a half to commemorate a Buddhist holiday and the death of his late father Bhumibol Adulyadej.
He has not commented on the demonstrations, despite tension in Bangkok as protesters grow bolder in their challenge to the royal institution.
But the king has made rare public visits with his supporters waiting outside the palace -- a charm offensive for an army of local and international media.
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