BANGKOK (AFP) -- Tens of thousands of protesters surrounded Thai Prime Minister Thaksin Shinawatra's office Tuesday to demand he step down, as the premier threatened a state of emergency if the demo turned violent.

The crowd, which police estimated at 60,000 people, was the biggest yet to join the weekly protests against Thaksin, prompting Bangkok police to mobilize its entire force to patrol the march.

One of the protest leaders, Thaksin's former political mentor Chamlong Srimuang, urged the demonstrators to remain peaceful but to seal off the premier's office and cause huge traffic jams in nearby roads.

"Don't go inside Government House, don't break its gates. Otherwise, we will fall into their trap. Please be assured that we are on the right track and will win in the end," he said.

Protesters included students, union workers, anti-globalization protesters and other activists.

Their plan was to blockade the building during the weekly Cabinet meeting, which Thaksin was set to hold by video conference from rural northeastern Thailand, where he was campaigning with his supporters.

Thaksin told reporters in the town of Ubon Ratchathani that he would declare a state of emergency in Bangkok if the protest turned violent.

"I am ready to sign, to impose a state of emergency rule, if necessary. Security ministers have agreed that they may need it to help them maintain order," he said.

"There was violence in the past, and many of those people are in the protest today," he told reporters.

Protest leader Chamlong led a 1992 popular uprising against a military government that restored democracy but cost scores of lives in a crackdown by security forces.

A senior security official said Monday that if an emergency were declared, authorities' first action would be to impose a curfew on the capital.

But the marchers made peaceful, even festive progress through central Bangkok as they walked about two kilometers (one mile) from a field near the royal palace to Thaksin's residence.

A sea of national and royal flags flowed with the protest, as people chanted slogans of non-violence.

"I'm quite sure of our victory," said garment worker Joe Chiwasanti, 38, as the marchers set out. "We won't quit" until Thaksin resigns, he added.

The march began after a noisy but peaceful all-night rally that drew some 60,000 people at its peak, according to police.

Thousands of the prime minister's supporters, meanwhile, were gathering on the northern outskirts of Bangkok to show their strength in the capital, raising fears of violent confrontations.

All 21,850 personnel in the metropolitan police were mobilized for the protest, with another 1,000 Special Branch police, commandos and border patrol officers deployed at Government House.

Simmering criticism of Thaksin's autocratic style exploded in late January, when his family earned 1.9 billion dollars by selling its 50 percent stake in telecom giant Shin Corp to a Singapore firm, using legal loopholes to avoid paying tax.

Despite the weekly rallies, Thaksin -- who easily won elections in 2001 and 2005 -- continues to enjoy widespread support among rural Thais who have benefited from his populist policies.

Thaksin called snap elections for April 2 in a bid to defuse the crisis but the main opposition are boycotting the polls, threatening to worsen the political turmoil.