Tens of thousands of Thai protesters marched on Government House in Bangkok on Tuesday to demand the resignation of Prime Minister Thaksin Shinawatra.
An estimated 50,000 protesters took part in Tuesday's rally
They surrounded the building ahead of the weekly cabinet meeting.
An estimated 20,000 police were put on standby amid warnings the rally could turn violent, but there were no reports of trouble.
The rally was the latest in a series of protests accusing Mr Thaksin of corruption and abuse of power.
Amid the escalating tension, the prime minister called a snap election for 2 April to try to regain authority, but the opposition has decided to boycott the poll.
Early on Tuesday morning about 50,000 marchers made their way from Sanam Luang field, near Bangkok's Grand Palace, down the broad road towards Government House.
Many of them had arrived at Sanam Luang on Monday evening, staying up the whole night to voice their displeasure at Mr Thaksin.
The protesters sang songs and held up banners reading "Thaksin Out " and "Change Through Peace", as they massed around Government House, where the weekly cabinet meeting was taking place.
Mr Thaksin was not at the meeting. Instead he chaired it from the north-east where he is campaigning ahead of the election.
Speaking to reporters from the city of Ubon on Tuesday, he vowed to declare a state of emergency if the protest turned violent.
But the rally organisers repeatedly insisted they intended to keep the protest peaceful, and the crowd so far appears to be well-disciplined.
One of the main protest leaders, former general Chamlong Srimuang, called for protesters to stay outside Government House until Mr Thaksin stepped down.
Another rally leader, media tycoon Sondhi Limthongkul, said: "We'll stay as long as it takes."
The demonstrators have held regular protests in recent weeks, with only one aim - to get Mr Thaksin to resign.
Criticism has intensified since his family sold its stake in Shin Corp, the company he built up before entering politics, for $1.9bn in January.
The sale triggered accusations of insider trading and tax dodges, and angered many Thais who saw an important national asset sold to Singaporean investors.