Protesters massed in front of a police barricade outside Wat Benjamabhopit, also known as the Marble Temple. Police fired teargas as some tried to heave aside concrete barriers.
"I just want the people named Shinawatra to get on a plane and go somewhere - and please, don't come back," said Chatuporn Tirawongkusol, 33, whose family runs a Bangkok restaurant.
Outside the Metropolitan Police Bureau, about 3,000 protesters rallied, accusing riot-clad police of being manipulated by Thaksin, a former policeman who rose to become a telecommunications magnate before entering politics and winning back-to-back elections in 2001 and 2005.
(Read more: Spotlight on Thailand as political strife escalates)
The area around Government House was a scene of nearly non-stop skirmishes, as police fired teargas into a stone-throwing crowd chanting "Slaves! Slaves!" A Reuters photographer saw protesters hurl at least a dozen petrol bombs into police positions from Rajamangala University of Technology Phra Nakhorn across a canal from Government House.
There was a mixture of anger and anxiety among protesters occupying the university. Some wheeled garbage bins full of stones to hurl at police, while others worried about a late-night operation to clear the campus by force.
"It's not safe here," said Sumittra, 40, a government official who didn't want her full name used. "We don't know when they will attack us."
Protest leader Suthep Thaugsuban urged government workers to go on strike on Monday and called on television stations to stop broadcasting state news.
"We invite all Thais to join us and defend democracy," he said in a speech televised live on all almost every station, including state-owned Thai PBS which agreed to broadcast the speech after protesters surged into its compound.
Capping a week-long bid to topple Yingluck and end her family's more than decade-long influence over Thai politics, Suthep had urged supporters to seize government offices, television stations, police headquarters and the prime minister's offices in a "people's coup".
Suthep, a deputy prime minister in the previous Democrat-led government that Yingluck's party beat in a 2011 election, told supporters they had occupied 12 state agencies and brought a million people on the streets. Police said about 30,000 people joined the protest on Sunday, compared with 100,000 a week ago.
Yingluck, who become Thailand's first female prime minister, has called for talks with the protesters, saying the economy was at risk after demonstrators occupied the Finance Ministry on Monday. Suthep has ignored her.
(Read more: Thai Finance Ministry occupied amid huge anti-government protests)
The Democrats, Thailand's oldest political party, have not won an election in more than two decades and have lost every national vote for the past 13 years to Thaksin or his allies.
Thailand faces its worst political crisis since unrest in 2010, which ended with a military crackdown. In all, 91 people were killed then, mostly Thaksin's supporters trying to oust the then-Democrat government. Suthep faces murder charges for his alleged role in the ordering crackdown.
Thaksin, who won over poor rural and urban voters with populist policies, was convicted of graft in 2008. He dismisses the charges as politically motivated and remains in close touch with the government from his self-imposed exile, sometimes holding meetings with Yingluck's cabinet by webcam.