Thailand's Prime Minister Samak Sundaravej has declared a state of emergency in the capital Bangkok, after clashes left at least one person dead.
Dozens more were hurt in the fighting early on Tuesday.
The clashes began after supporters of Mr Samak pushed through police lines near Government House, occupied by the People's Alliance for Democracy.
PAD supporters say the government is a front for the exiled former Prime Minister, Thaksin Shinawatra.
The prime minister said that emergency rule would not last long.
"No one has the right to do such a thing as they have done," said Mr Samak, in a televised press conference.
"I had no other choice but to declare a state of emergency in Bangkok in order to solve the problem for once and for all.

"The military and police will carry out the implementation."
Mr Samak put the army commander, General Anupong Paojinda, in charge of enforcing the state of emergency in the capital. The general now has special powers to:
detain and remove people from any location
deploy troops to help police maintain order
ban gatherings of more than five people
impose restrictions on media reports that could "undermine public security".

South Korea and Singapore have advised their citizens against any non-essential travel to Thailand.
The PAD leader said protesters occupying the government's building had refused to move, despite the state of emergency.
"There are not enough jails to put us all into," Chamlong Srimuang told thousands of PAD demonstrators.
An emergency debate in parliament earlier failed to end the stalemate between Mr Samak's fragile coalition and his opponents.

Troops deployed
Overnight, thousands of PAD supporters took to the streets of Bangkok and forced their way into government buildings.
Mr Samak was initially praised for his restraint in dealing with the protests, but he suddenly found his position weakened on Friday when the police pulled back and the triumphant protest leaders were left in control of the government complex.
The demonstrations in the capital remained relatively peaceful over the weekend, but early on Tuesday violent clashes broke out when hundreds of government supporters marched towards Government House, armed with sticks and clubs.
TV pictures showed a man lying motionless on the ground with a pool of blood around his head as well as dozens of injured afterwards.
Dr Petchpong Kamjornkijjakarn of the Erawan Medical Centre said one person had died from severe head injuries and that four others were in a serious condition, two of whom had gunshot wounds.
At least 31 others are being treated for injuries across the city.
On Monday, public sector unions said they would begin a nationwide strike at 43 state enterprises on Wednesday unless the prime minister stepped down.
The State Enterprise Workers Relations Confederation also threatened to cut off water, electricity and phone service at government offices and disrupt flights.
The BBC's Jonathan Head in Bangkok says there appear to be very few ways out of this crisis.

KEY EVENTS
Sept 2006: Bloodless coup by military sees PM Thaksin Shinawatra removed from office
April 2007: New military-drafted constitution approved
Dec 2007: General election won by People Power Party (PPP), seen as reincarnation of Thaksin's now banned Thai Rak Thai party
Jan 2008: Samak Sundaravej chosen as PM
Feb 2008: Thaksin returns from exile
May 2008: PAD protests against Samak begin
July 2008: Thaksin goes on trial for corruption; his wife is found guilty of fraud. By mid-August the family has fled to the UK
August 2008: PAD protests escalate

The government retains strong rural support and would probably be re-elected if fresh polls were called - and the PAD does not support such elections, our correspondent says.
Meanwhile, the revered King Bhumibol has also refused to intervene.
The PAD - a loose grouping of royalists, businessmen and the urban middle class - was formed in the months before Mr Thaksin was ousted by a military coup in 2006. He has since fled the country to avoid facing trial over corruption charges.
It has a passionate following in various parts of the country, especially Bangkok, and some powerful backers among the elite.
But it has little support in most of rural Thailand, which voted strongly for Prime Minister Samak, and Mr Thaksin before him.

BANGKOK, Thailand (CNN) -- Thai demonstrators have called for a general strike Wednesday, as state media reported the ruling by Thailand's election commission that Prime Minister Samak Sundaravej's People's Power Party should be dissolved for allegedly trying to buy votes.

Thailand's embattled prime minister gave no indication Tuesday that he intends to forcibly stop anti-government street protests that have paralyzed the government and left one person dead.

Samak said in an exclusive interview with CNN: "Now we are waiting. I think by now that I have done everything that a government can do to be soft and gentle."

But when asked if now is the time for the government to harden its stance, Samak said, "No."

The protesters -- who have occupied Samak's office for a week -- are demanding the Thai prime minister step down, accusing him of being a proxy for his ousted predecessor, Thaksin Shinawatra.
Samak strongly denied that Thaksin was "still pulling the strings."

"You don't you use this word to me," he told CNN's Dan Rivers. "This is an insult to me."

Samak spoke to CNN hours after he declared a state of emergency in the capital city of Bangkok in response to overnight clashes between his supporters and anti-government demonstrators that wounded 40 and left one person dead.

It was the worst outbreak of violence since the People's Alliance for Democracy (PAD) launched its efforts to oust Samak.

The state of emergency order -- which overrides the country's constitution and allows the army to be in charge of enforcing laws -- forbids public gatherings of more than five people and bans the media from publishing or broadcasting images that would panic the public.

But protest leader Sondhi Limthongku said the government order will not deter his supporters from continuing their movement to oust Samak.

"We are sending a strong message to all politicians: Do not ever think that if you win the majority, you can do anything simply because you claim you win the majority," said Sondhi, who is head of PAD. "This is wrong."

The protesters, who last week shut down three airports across the country, have said they plan to do the same to Bangkok International Airport. A shut-down there would cause major disruptions because many international travelers use it for connecting flights.

"We're closing that airport only temporarily, just for a symbolic gesture," Sondhi said.

Demonstrators have also called for a general strike Wednesday, and more than 40 unions have agreed to participate -- potentially paralyzing the country.

Protesters also continued to occupy Government House, the government's headquarters.

PAD contends Samak is trying to amend the constitution so Thaksin -- who was ousted in a coup in 2006 -- does not have to face charges. Thaksin returned to England this month, just as he was to appear in court in a corruption case.

Thailand's election commission ruled Tuesday that Samak's People's Power Party should be dissolved for allegedly trying to buy votes in the December elections, state media reported.

Thai political analyst Thitinan Pongsuthirak said the commission's unanimous decision, which is not expected to have any immediate effect, has wider implications for Thailand.

"This is a big test not just for Samak but it's a litmus test for Thai democracy and Thai society," Thitinan said.

The ruling stems from charges against the party's deputy leader, Yongyuth Tiyapairat, who the Supreme Court found guilty of buying votes during the campaign phase of last year's elections.

According to the country's constitution, senior members of a party that is ordered dissolved cannot participate in political activities for five years. Other members have to find a new party within two months, the Thai News Agency said.

The news agency added that PPP members have already registered a new political party, which is expected to be housed in a building owned by Thaksin