Tens of thousands of pro-democracy protesters massed close to Thailand's Grand Palace on Saturday, in a huge rally calling for PM Prayut Chan-O-Cha to step down and demanding reforms to the monarchy.
The kingdom has seen near-daily gatherings of youth-led groups since mid-July calling for the resignation of Prayut, the former army chief behind the 2014 coup, and a complete overhaul of his administration.
Some are also demanding reforms to Thailand's ultra-wealthy and powerful monarchy -- a once-taboo topic in the country due to its tough royal defamation laws.
The burgeoning movement, partly inspired by Hong Kong's pro-democracy protests, remains largely leaderless.
But this weekend's demonstration was organised by students of Bangkok's Thammasat University -- a group that has been among the most vocal about the royal family's role in Thailand.
Among the crowd at the historic Sanam Luang field in front of the Grand Palace, history teacher Patipat, 29, said the government wouldn't be able to ignore the demonstrators.
"Today is one of the turning points in Thai history," he told AFP.
By nightfall more than 18,000 protesters had gathered around the university's downtown campus and the surrounding area, according to Bangkok's Metropolitan Police Bureau, though protest organisers claim a much higher turnout.
AFP reporters on the ground estimated a crowd size closer to 30,000.
This would make it one of the largest gatherings the kingdom has seen since the 2014 coup.
Streaming into the Sanam Luang field, LGBT activists unfurled rainbow flags as protesters marched in, giving the three fingered salute from the Hunger Games trilogy that has been widely adopted by pro-democracy demonstrators.
They huddled under a sea of umbrellas to shield from rain, their glowing smartphones bobbing in the darkness above the 12-hectare grassy field.
"We are calling for Prayut Chan-O-Cha... to resign immediately," prominent activist and protest organiser Parit Chiwarak, also known as "Penguin" told AFP.
Student leaders also reiterated their demands for reforming the monarchy "to adapt it to society".
"We will not stop until we have monarchy reform," said fellow activist Panusaya Sithijirawattanakul.
Around 10,000 uniformed and plainclothes police patrolled the area as the crowd grew through the day.
Some protesters wore fake crowns, while a group carried a cardboard model of a submarine to symbolise their displeasure over military spending.
Demonstrators have said they will continue rallying overnight at Sanam Luang before marching to Government House on Sunday morning -- a move authorities have warned against.
- Pro-democracy test -
A cycle of violent protests and coups has long plagued Thailand, with the arch-royalist military stepping in to stage more than a dozen putsches since the end of royal absolutism in 1932.
The latest wave of student-led demonstrations has largely been peaceful.
But unprecedented calls for frank discussions about the monarchy have sent shockwaves through the kingdom.
King Maha Vajiralongkorn sits at the apex of Thai power, buttressed by the kingdom's military and billionaire clans, and commands an estimated fortune of up to $60 billion.
The student demands include greater accounting of the palace's finances, the abolition of royal defamation laws and for the king to stay out of politics.
They also want a rewrite of the 2017 military-scripted constitution, which they say tilted last year's election in Prayut's favour, and for the government to stop "harassing" political opponents.
So far, authorities have arrested more than two dozen activists, including "Penguin", charging them with sedition before releasing them on bail.
The weekend demonstrations will prove a test for the pro-democracy movement, analysts say, who question if its support base will grow beyond the social media-savvy youth.
Bangkok businessman Warren, 50, joined the rally Saturday with his wife.
He has a university-aged daughter and is concerned about her future.
"We need to reform every institution in Thailand -- monarchy, army, education," he told AFP, wearing a pro-democracy T-shirt that matched his wife's.
Thammasat University, where protesters gathered Saturday, has long been a hotbed of student activism.
In 1976 students at the university protesting the return of a military dictator were shot, beaten to death and lynched by state forces and royalist mobs.
Prayut has vowed authorities would use "soft measures" on the protesters "because they are children".
Demonstrators gathered Tokyo, Stockholm, and Taipei Saturday in solidarity with the Bangkok protesters, with further rallies planned in a dozen countries, including the United States and France.