Singing pro-democracy songs, dancing, hooting horns and waving placards, red-shirted supporters of former premier Thaksin Shinawatra flooded streets in Bangkok's historic heart and threatened to stay for a week.
Most traveled from Thailand's poor, rural provinces, piling into pick-up trucks, cars and even river boats, and illustrating Thaksin's enduring influence on Thai politics even after his ouster in a 2006 coup, graft conviction and self-exile.
Protest leaders hope a powerful display of popular support will force Prime Minister Abhisit Vejjajiva to dissolve parliament and call an election that Thaksin's allies would be well-placed to win. They also want to convince wavering partners in the governing coalition to break away.
"Brothers and sisters, don't give up. Don't fight for me. Fight for the country," Thaksin told supporters via video link from an undisclosed location in Europe.
"I am a symbol of those bullied by the elite who do not care about democracy and justice." The turbulence adds to a seemingly intractable political crisis that pits the military, urban elite and royalists who wear yellow at protests and strongly back Abhisit against mainly rural Thaksin supporters who wear red and say they are disenfranchised.
The "red shirts" plan to gather on Monday morning at a military base where Abhisit has taken refuge and is coordinating security. If their demands are not met, they have threatened to march through Bangkok, raising the prospect of paralyzing many of the capital's already-congested streets.
Abhisit is widely expected to survive the showdown.
He must go to the polls by the end of next year. In his weekly television address on Sunday, Abhisit indicated immediate elections were unlikely, citing the tense political climate and his coalition government's parliamentary majority.
Several main roads near government offices were blocked off either by protesters' pick-up trucks and motorcycles or cordoned off by police and soldiers. Authorities deployed 50,000 police, soldiers and other security personnel across the city.
"We're asking the government to relinquish power and return it to the people," said Veera Musikapong, chairman of the protest group, United Front for Democracy against Dictatorship, setting a deadline of noon Monday for parliament to be dissolved.
Deputy Prime Minister Suthep Thuagsuban said protesters must not disrupt life for Bangkok residents. "If they close every road, that will be illegal," he told reporters.
Last April, protests by Thaksin supporters triggered Thailand's worst street violence in 17 years. In recent months, they have emphasized non-violence - and Thaksin's rhetoric has softened since last year when he spoke of a "revolution." But without causing a big disruption, they may have trouble forcing elections, said Charnvit Kasetsiri, a political historian at Thammasart University.
"It's hard to pressure the government if the crowd is under control. They will have to try to step it up in the next few days to make more noise and make themselves heard. The danger for the reds is that the government could just wait it out," he said.
The protesters say the British-born, Oxford-educated Abhisit came to power illegitimately, heading a coalition the military cobbled together after courts dissolved a pro-Thaksin party that led the previous coalition government.
They chafe at what they say is an unelected elite preventing allies of twice-elected Thaksin from returning to power through a vote. Adding to their anger, Thailand's top court seized $1.4 billion of Thaksin's assets last month, saying it was accrued through abuse of power.
"This government angers me. I never cared much about politics until a few years ago when it became so clear they are trying to hold onto power at the expense of people like us," said Teerachai Sukpitak, a farmer from northeast Leoi province.
Thailand was plagued by political upheaval in 2008 when yellow-shirted protesters who opposed Thaksin's allies in the previous government occupied the prime minister's office for three months and then blockaded Bangkok's international airport until a court ousted the government.
Thaksin, a 60-year-old former telecommunications tycoon, is beloved in the vote-rich north and northeast after becoming the first Thai leader to win landslide elections twice, largely by reaching out to the poor through populist policies such as universal healthcare and cheap loans.
His critics accuse him of authoritarianism, corruption and undermining the monarchy - charges which he has denied.
The political conflict has done little to stop foreign investors, who have snapped up about $500 million of Thai stocks this year and are more focused on a swift, export-led economic rebound in Southeast Asia's emerging markets.
