Raucous, whistle-blowing crowds have besieged government buildings in Bangkok to challenge Yingluck and her exiled brother, ousted former premier Thaksin Shinawatra, in the biggest protests since mass street rallies in 2010 that turned deadly.
Demonstrators also rallied outside at least a dozen provincial halls mainly in the opposition's southern heartlands -- including on the tourist island of Phuket.
The turmoil comes as Yingluck's embattled government faces a no-confidence motion in parliament introduced by the opposition Democrats, who have not won an elected majority in about two decades.
While the demos have so far been largely peaceful, there are fears they could descend into another bout of street violence in a country that has seen several episodes of political unrest since Thaksin was ousted in a 2006 coup.
The billionaire tycoon-turned-politician is adored by many of the country's rural and urban working class. But he is reviled by many in the elite and the middle classes, who accuse him of being corrupt and a threat to the monarchy.
Up to 10,000 protesters gathered Wednesday at a large office complex on the northern outskirts of Bangkok that houses several key government agencies, according to an AFP reporter at the scene.
Their numbers swelled dramatically as protest leader Suthep Thaugsuban marched into the compound, flanked by thousands of other demonstrators.
"We are very upbeat and I think we will win in a few days," the former deputy premier and key opposition figure told reporters earlier as he left his de facto headquarters at the occupied finance ministry.
A defiant Suthep on Tuesday called for the creation of an unelected administration to run the country, in the clearest indication yet that the demonstrators are seeking to suspend the democratic system.
"If we demolish the Thaksin regime ... we will set up a people's council which will come from people from every sector," he said. "Then we will let the people's council pick good people to be the prime minister and ministers."
Arrest warrant
On Tuesday protesters surrounded the interior, agriculture, transport, and sports and tourism ministries, ordering officials inside to leave, a day after occupying the finance and foreign ministries.
"The situation is serious but it is under control," Pracha Promnog, a deputy prime minister, told reporters after a meeting with the premier.
But he warned protesters would not be allowed to occupy Government House or parliament.
A court has issued an arrest warrant for Suthep for his role in the ministry seizures and authorities have urged the veteran politician to surrender.
The recent protests were sparked by plans by the ruling Puea Thai party to introduce an amnesty that could have allowed the return from self-imposed exile of Thaksin.
The Senate blocked the controversial bill but demonstrators have since broadened their goal and now want to topple the government.
Yingluck on Monday ordered the expansion across Bangkok of the Internal Security Act, which gives authorities additional powers to block routes, impose a curfew, ban gatherings and carry out searches.
Her party, which holds a comfortable majority, is expected to win the censure vote expected later in the week.
One option could be for Yingluck to dissolve the lower house afterwards and call fresh elections, knowing that Pro-Thaksin parties have won every election for more than a decade.
She appears reluctant to resort to force to evict the protests given the bloodshed which erupted in 2010, when more than 90 people died in a military crackdown on pro-Thaksin protests under the previous government.
The possibility of military intervention also constantly looms over Thailand, which has seen 18 actual or attempted coups since 1932, but the army has so far shown no sign that it is preparing to get involved.
Yingluck's Red Shirt supporters, who have held their own rally at a sports stadium in the capital, appeared to be losing patience with the growing protests although they have refrained from taking to the streets.
"The current situation is near breaking point," said Red Shirt leader Jatuporn Prompan, calling for more supporters to join their gathering.
But "we will only move out (on to the streets) if there's a coup," he added.
--AFP
Catat Ulasan