Anti-government protesters have forced the evacuation of Thailand's top crime-fighting agency, on the fourth day of street demonstrations.
The marchers, who want the government to step down, targeted a complex of government offices outside the city.
The protest leader said they wanted to shut down government ministries in a bid to cause disruption.
They accuse the government of being controlled by the prime minister's brother, Thaksin Shinawatra.
The BBC's Lucy Williamson in Bangkok says the mood of the protesters is very friendly, as they and the government side shadow-box around each other.
Prime Minister Yingluck Shinawatra's secretary general, Suranand Vejjajiva, told the BBC that there were no plans to use the army.
"We are reassured that the police can handle the situation as the protesters are peaceful and do not create any violence," he said.
'Seize city hall'
The protests are being led by former opposition Democrat Party lawmaker Suthep Thaugsuban, for whom police have issued an arrest warrant.
They began on Sunday and so far have targeted the finance, foreign and interior ministries, among others.
"Let the people go to every ministry that remains to make civil servants stop serving the Thaksin regime,'' the Associated Press news agency quoted him as saying.
"Once you take over, civil servants can no longer serve the Thaksin regime. Brothers and sisters, go seize the city hall."
Despite the arrest warrant, police made no attempt to detain him as he led protesters to government offices.
On Wednesday afternoon, hundreds of protesters surrounded the Department of Special Investigations (DSI), which is Thailand's equivalent of the US Federal Bureau of Investigation.
The DSI is a particular target for the demonstrators - they accuse its chief of conducting partisan investigations against opponents of the government, says the BBC's Jonathan Head in Bangkok.
The DSI chief ordered his staff to leave as protesters surrounded the building, Reuters news agency said.
However, Mr Suranand said that the government house itself was secure and the government still functioning.
Government supporters were organising their own demonstrations around the country, he added.
Ms Yingluck - who on Monday invoked special powers allowing officials to impose curfews - said that the government would not use force against protesters.
"This is not the 'Thaksin regime', this is a democratically elected government," she told media outside parliament.
The demonstrations are the biggest to hit Thailand since the violence in early 2010, when supporters of Mr Thaksin paralysed key parts of Bangkok.
More than 90 people, mostly civilian protesters, died over the course of the two-month action.
In the wake of those events, a government led by Ms Yingluck and the Pheu Thai party was elected, mostly by rural voters who benefited from Mr Thaksin's policies.
But many urban and middle class voters are bitterly opposed to him.
They say he controls the current government from self-imposed overseas exile.
They have been angered by now-shelved political amnesty legislation that they say could have allowed his return without serving a jail sentence for corruption.
Until now, the government and the police have chosen not to confront the protesters, in the hope that the movement will run out of steam, our correspondent adds.
That is not happening yet, and protest leaders insist they will not stop until the government is forced from office and replaced by what they call a People's Council.
But a more likely scenario would be a fresh general election - and the governing party, which has won the last five, would probably win again, our correspondent adds.