Thai police allowed opposition protesters through barricades outside the government and metropolitan police headquarters Tuesday, sharply easing tensions after two days of violent clashes aimed at ousting Prime Minister Yingluck Shinawatra.

The reason for the sudden thaw in hostilities was not immediately clear but it came after police said they would no longer use force to defend their Bangkok headquarters from thousands of anti-government protesters who marched on the high-profile target.

Demonstrators were allowed to approach the perimeter fence of Government House with no resistance from security forces. Dozens of protesters also streamed into the police building where they were seen shaking hands with officers, AFP reporters saw.

Metropolitan Police chief Lieutenant General Kamronwit Thoopkrajang said his officers would no longer try to fend off protesters at the police base.

"The Metropolitan Police Headquarters belongs to the public," he told AFP.

"There will be no use of tear gas today," he said. "Last night a police officer was injured by a gunshot so if we resist there will be more injuries, and we are all Thais," he said.

The protests, aimed at unseating the elected government and replacing it with a "people's council", are the latest bout of unrest in the kingdom since royalist generals ousted Yingluck's brother Thaksin Shinawatra in a coup seven years ago.

It is the kingdom's worst political violence since a deadly military crackdown on pro-Thaksin "Red Shirts" rallies in 2010, although the recent clashes have been largely confined to certain parts of the city, away from main tourist districts.

On Monday police used rubber bullets, tear gas and water cannon to fend off rock-throwing demonstrators for a second day at the government and police headquarters, after weekend unrest that left several dead and scores wounded.

Thailand's long-running political conflict broadly pits a Bangkok-based elite backed by the military and the palace against rural and working class voters loyal to Thaksin, a billionaire businessman turned premier.

The latest battle played out on the streets of Bangkok has pitted a shrinking band of hardcore protesters against pro-Thaksin political forces who have won every election in more than a decade, most recently in 2011 under Yingluck.

In her first televised address since the weeks-long protests descended into violence at the weekend, Yingluck said Monday that the protest leader's demands were unconstitutional.

The embattled premier said she would have considered resigning or calling an election if her opponents had not already ruled out these moves as insufficient. She insisted the government was open to "every option" to restore peace.