Anti-government protesters crossed heavily fortified barriers and reached the gates of the Thai Prime Minister's office and the city police headquarters without resistance from police.
Police used cranes to remove concrete slabs and barbed wire barricades on a road leading to the police headquarters after agreeing to let the protesters into the building.
After bitterly resisting them with tear gas and rubber bullets since Saturday, police also stood by as protesters removed the barriers to the prime minister's office and walked through on Tuesday.
The unexpected reversal of strategy by the government suggests it no longer wants to confront the protesters after three days of clashes that have left three people dead and more than 230 injured and raised concerns about the country's stability.
Government officials did not comment on the developments, and it was not clear if this would provide more than a lull to the violence and the crippling political deadlock that undermines Thailand's democracy, economy and tourism.
After breaching the barriers on the road, the protesters milled outside the gates of the prime minister's office, known as Government House, and made no attempt to go through the gray gates of the sprawling compound.
''This is a victory for us. This is a victory for the protesters,'' said Kusol Promualrat, wearing a military camouflage green jacket, standing in front of the gate.
The police pulled back ''because they know that if this doesn't stop more people will get hurt, more people will die.''
On Monday night, protest leader Suthep Thaugsuban told his supporters to storm the Bangkok Metropolitan Police Bureau, one of the main buildings they have vowed to seize as part of a campaign to topple the government of Prime Minister Yingluck Shinawatra.
At the same time, Yingluck told a news conference that while she is willing to do anything it takes to end the violent protests, she cannot accept Suthep's demand to hand power to an unelected council.
Yingluck was elected with an overwhelming majority in 2011, and many observers see the protesters' demand as unreasonable if not outlandish.
In some of the worst clashes since the protests began last week, on Monday protesters commandeered garbage trucks and bulldozers, and tried to ram concrete barriers at the Government House and other offices.
Police repelled them by firing tear gas, water cannons and rubber bullets, as protesters shot back explosives from homemade rocket launchers.
The protesters, mostly middle-class Bangkok supporters of the opposition Democrat Party, accuse Yingluck of being a proxy for her elder brother, former Prime Minister Thaksin Shinawatra.
He was deposed in a 2006 military coup but remains central to Thailand's political crisis, and is a focal point for the protester's hatred.
The protesters say their goal is to uproot the political machine of Thaksin, who is accused of widespread corruption and abuse of power.
The violence has largely been near the Government House, the Parliament and Metropolitan Police Bureau in the historic quarter of the capital.
The area has some of Bangkok's main tourist attractions such as the Grand Palace, Wat Pho temple, the Bangkok zoo, and the backpacker area of Khao San Road.
Most of Bangkok, a city of 10 million, has been unaffected. Yingluck and Suthep met briefly on Sunday in the presence of top military leaders, even though he had an arrest warrant against him.
A second arrest warrant was issued Monday on charges of insurrection. His campaign has raised suggestions he may have the backing of the military, which has long had a powerful influence over Thai politics.
The army has often stepped in during times of crisis, carrying out 18 successful or attempted coups since the 1930s.
Political instability has plagued Thailand since the military ousted Thaksin, who remains hugely popular among rural voters, in 2006.
Two years later, anti-Thaksin protesters occupied Bangkok's two airports for a week after taking over the prime minister's office for three months, and in 2010 pro-Thaksin protesters occupied downtown Bangkok for weeks in a standoff that ended with parts of the city in flames and more than 90 dead.
Tourism and Sports Minister Somsak Pureesrisak told reporters he has set up an agency to help tourists in Thailand.
He said the target of 26.5 million tourists for the year may not be met.