'It is wrong for protesters to take the entire Thai nation hostage,' Mr Somchai said in a televised address to the nation.

'The government is not intending to hurt anybody but is just facilitating official works, and the emergency will be temporary,' he added.

In his address, Mr Somchai said police and some military units would try to end the blockades by the People's Alliance for Democracy (PAD) at the Suvarnabhumi and Don Muang airports which he said was causing massive damage to the economy.

Mr Somchai called on the army to back up police in enforcing the state of emergency at the airports.

Protesters from the People?s Alliance for Democracy (PAD) movement, which seized control of Suvarnabhumi on Tuesday night and blockaded Don Mueang earlier on Thursday, swiftly vowed to defy the state of emergency.

'We will not leave. We will use human shields against the police if they try to disperse us,' PAD leader Suriyasai Katasila told Reuters.

Another key PAD leader, Chamlong Srimuang told protesters at government offices in central Bangkok, 'We are in the very, very final moment of our fight for democracy with the king at the head of state so I ask all the protesters not to panic.' Anti-government protestors have occupied the government offices since August.

He said that if police broke up the rallies on Thursday night 'just come back the next morning and take over these strategic locations.'

It was not clear what action the police might take, but 30 medical teams were on standby in case of a bloody crackdown, the Nation newspaper's website said.

Some office employees left work early in Bangkok and the United Nations advised its staff to go home and remain indoors.

Deputy Agriculture Minister Thirachai Sankaew told Reuters after a cabinet meeting earlier that the cabinet agreed to use the emergency decree at the two airports to bring the situation back to normal.

He said emergency laws will apply to areas around the main international Suvarnabhumi airport and the domestic Don Muang airport.

An emergency decree gives the military the right to restore order, allows the suspension of civil liberties, bans public gatherings of more than five people and bars the media from reporting news that causes panic.

Thousands of anti-government protesters are occupying the terminals of both airports, forcing the cancellation of all flights in and out of the capital.

Bangkok's Suvarnabhumi international airport, which has been occupied by anti-government protesters, will remain closed until at least 6.00 pm (7.00pm Singapore time) on Saturday, the airport authority said on Thursday.

'Protesters are still rallying in front of the terminal for the third consecutive day with no sign of dispersing, therefore the authority has to prolong the closure,' an Airports of Thailand (AOT) statement said.

The authority said that Bangkok's old Don Mueang airport, which handles some domestic services, will stay closed until at least Friday.

'Passengers should not travel to either airport until they resume operations,' the statement added.

Mr Somchai earlier called an urgent cabinet meeting after demonstrators seized Suvarnabhumi international airport on Tuesday night and blockaded the old Don Mueang airport early on Thursday.

The Thai Cabinet met outside the capital to evade anti-government demonstrators and weighed whether to impose a state of emergency to try to end airport protests that have left thousands of travelers stranded for two straight days.

Meeting with the prime minister in Chiang Mai, 570 kilometres north of Bangkok, the Cabinet considered both an emergency decree or the use of a tough internal security law, government spokesman Nattawut Sai-kua said.

'We have to consider these legal options to solve the crisis,' he said before the afternoon meeting.

The security law is a separate measure that would enable officials to bar public assembly and 'suppress' actions considered harmful to national security.

There also was speculation in the Thai media that the prime minister might remove the powerful army chief, General Anupong Paochinda, who called on Wednesday for the dissolution of Parliament and new elections to resolve the deepening political crisis.

The anti-government protests, which gathered pace three months ago, have paralysed the government, battered the stock market, spooked foreign investors and dealt a serious blow to the tourism industry.

The crisis worsened early on Thursday as authorities shut down the Don Muang domestic airport, which had been receiving some diverted flights from Suvarnabhumi.

Mr Serirat Prasutanont, chief of the Thailand Airport Authority, said authorities feared protesters who stormed the Don Muang terminal might harm passengers and aircraft.

He said authorities were alerting airports nationwide to be ready to receive diverted flights. Thai Airways said one of its flights from Los Angeles landed on Thursday at U-Tapao air force base, 140 kilometres south-east of Bangkok.

The closure of the two airports left thousands of foreign tourists stranded, including Americans trying to get home for their Thanksgiving holiday on Thursday.

Thai government supporters earlier on Thursday urged Mr Somcha to declare a state of emergency, as activists who oppose the administration occupied a second Bangkok airport.

'We are calling for the government to declare a state of emergency in today's cabinet meeting,' Mr Jatuporn Prompan, a lawmaker from the ruling People Power Party told AFP.

'It's up to Prime Minister Somchai's judgment whether to invoke such a law or not,' he added.

Thailand's political crisis deepened overnight after Mr Somchai rejected a call by the powerful army chief to hold new elections, and as protesters captured Bangkok's domestic Don Mueang airport.

Anti-government protesters from the so-called People's Alliance for Democracy have demanded Mr Somchai's resignation, saying his administration is controlled by ousted former premier Thaksin Shinawatra, who lives in exile.

'If after an emergency is declared army chief Anupong Paojinda is still inactive or launches a coup against the government, then more than 100,000 of us will take to the streets immediately to protect the government,' he said.

Mr Jatuporn said pro-government supporters - who showed their strength on Nov 1 when 100,000 gathered in a Bangkok stadium to listen to an audio address from Thaksin - feared the crisis would end in clashes.

Fighting between rival camps in Chiang Mai on Wednesday left a PAD member dead.

'We are ready at any minute,' Mr Jatuporn said.

The pro-government camp, whose members usually wear red to distinguish themselves from the yellow clothes chosen by their foes, are set to rally in Bangkok on Dec 13 when Thaksin has promised to phone in. -- AFP, AP, REUTERS