"Thaksin, get out!" the protesters chanted as a band played protest songs and nearly 5,000 police officers stood guard. Police said they feared "troublemakers" would try to hijack the event.

Three hours into the rally, a crowd of about 30,000 had gathered near Thaksin's office in Government House. Many wore yellow headbands that said "Save The Nation."

Organisers anticipated the protest would exceed several others that have drawn up to 100,000 people. Thaksin's foes have been demonstrating almost daily for two weeks. They say he is corrupt and has abused his powers.

"We are here to fire Thaksin from the office," said Wanwipha Maenmanede, a 45-year-old employee of the state power company who came to the rally with her husband and 13-year-old daughter. "He is the most corrupt prime minister in the country's recent history."

Meanwhile, about 30,000 monks planned to gather Saturday evening at a field near the Grand Palace, the former royal residence, to pray "for peace and unity," said Gen. Chainat Yatchimplee, one of their leaders.

The three main opposition parties, who have said they will boycott the April 2 vote unless Thaksin resigns, appeared to be looking for a compromise to the political crisis.

Democrat party leader Abhisit Vejjajiva said he had proposed to Thaksin that he resigns and allows the king to appoint an interim government. Then the parties could call another election, which Thaksin "is welcome" to join, Abhisit told supporters Friday.

Aekkaporn Rakkhamsuk, a spokesman for the ruling Thai Rak Thai party, said the appointment of an interim government would violate the constitution and the country's "political tradition."

In a sign that the elections are likely to go ahead, the king's chief adviser, Gen. Prem Tinsulanonda, cast his ballot Saturday. Those registered can vote this weekend ahead of the ballot, which Thaksin hopes will give him a fresh mandate.

Prem did not comment after leaving the polling station.

Protest leader Chamlong Srimaung said he would ensure Saturday's rally was peaceful but that demonstrators would continue to hound Thaksin until he steps down. He said demonstrators would march on Sunday to Thaksin's house and hold rallies outside shopping malls in Bangkok.

"We will not march to the palace or any place that disturbs the royal family but will go wherever Thaksin goes to pressure him to resign and appeal to the king to appoint the interim government," Chamlong said.

Large numbers of people from southern Thailand where a Muslim insurgency has left more than 1,300 dead in the past two years were heading to the Thai capital for the rally, said Gen. Jumpol Manmai, head of the National Intelligence Agency.

Outside of Bangkok, Thailand's south is the only part of the country where Thaksin does not enjoy widespread support. His government is accused of committing rights abuses in an effort to quell the insurgency.

Thaksin has vowed to call a state of emergency if protests turn violent. He has campaigned across the country this week, telling voters that he would not bow to mob rule and that his government has brought universal health care and a healthier economy.

The king's top advisers have publicly called for calm and dialogue, but the palace has otherwise kept its distance from the fray because the king is not supposed to get involved in politics.

He has, however, stepped in to resolve national crises in the past, most recently in 1992 after street demonstrations against a military-backed government were violently suppressed.

Months of small anti-Thaksin rallies blossomed into a mass movement after the prime minister's family in January announced it had sold its controlling stake in telecommunications company Shin Corp. to Singapore state-owned investment company Temasek Holdings for a tax-free $1.9 billion.

Critics allege the sale involved insider trading and complain that a key national asset is now in a foreign government's hands. Thaksin is also accused of cracking down on dissent and stifling press freedom.