Thousands of protesters on Wednesday massed at Bangkok's main ministerial complex in an effort to paralyze the government and force reforms to Thailand's political system, dpa reported.
Protest leader Suthep Thaungsuban led a march of more than 10,000 demonstrators on a cluster of ministries in northern Bangkok.
The protesters gathered outside the Government Agencies Centre in north Bangkok, demanding the resignation of Prime Minister Yingluck Shinawatra and her cabinet.
Suthep has been encouraging his followers to occupy ministries to paralyze the government since Monday, when he seized the Budget Bureau that disperses civil servants' salaries.
He has called on civil servants to stop work and join the protest.
Hundreds of employees of the state-owned Telephone Organization of Thailand (TOT) welcomed the protests by blowing whistles and shaking rattles.
"To speak frankly, I don't like this government," said one female TOT employee who asked to remain anonymous. "There have been a lot of irregular practices under their administration."
Abhisit Vejjajava, leader of the opposition Democrat Party, claimed that corruption had doubled under the two-year administration of Yingluck during a censure debate that has coincided with the street protests.
The demonstrators said they hoped to close down the Labour, Industry, Justice, Science and Technology, Commerce and Public Health Ministries, but most had barred their doors.
On Tuesday, protesters surrounded and effectively stopped work at the Tourism, Agriculture and Transport Ministries.
Yingluck placed the capital under the Internal Security Act on Monday, which allows police to block protesters from entering restricted areas.
"The imposition of the special law is not intended to harm anyone because the government will not use violent means to deal with the protesters," Yingluck said, according to the Bangkok Post.
Suthep, a former senior member of the opposition Democrat Party who resigned from parliament to lead the protests, has vowed to rid the government of the influence of fugitive former prime minister Thaksin Shinawatra, Yingluck's brother who is considered the de facto leader of the ruling party.
Suthep said he would not stop the protest even if Yingluck resigned and dissolved parliament, leading some observers to accuse Suthep of paving the way for an "unconstitutional" power seizure.
"If there is no military coup there will have to be a people's coup," said Education Minister Chaturon Chaisaeng. "If the people seize all the ministries and the government is paralyzed, maybe they will try to set up some sort of an Assembly of the People."
There have been 18 military coups in Thailand since the overthrow of the absolute monarchy in 1932, the latest in 2006 to oust Thaksin.
Given the international condemnation the last coup triggered, it was unlikely that the army would intervene unless there is street violence, political observers said.
The protesters are a coalition of anti-Thaksin groups.