The protesters have paralysed Bangkok's international airports
Thai opposition protesters occupying Bangkok's two main airports say they are prepared to defend themselves against any police operation.
A protest leader at the domestic Don Mueang airport said the demonstrators would "fight to the death".
Emergency rule has been declared around the two airports, where thousands of passengers have been left stranded.
Police appear prepared to take action to stop the protests but made no move to do so overnight, say correspondents.
The BBC's Jonathan Head at Suvarnabhumi international airport said ambulances and police lorries were at the scene but the expected assault has not taken place.
The presence of children and elderly people among the demonstrators may have been one reason for this, as well as the continuing refusal of the army to get involved, says our correspondent.
The protesters, from the People's Alliance for Democracy (PAD), have said they will not leave until Prime Minister Somchai Wongsawat resigns.
Earlier this week, Thai army chief Gen Anupong Paochinda urged Mr Somchai to call a snap election as a way of easing the crisis, fuelling speculation that a coup could be imminent.
Mr Somchai will remain in Chiang Mai indefinitely for his own safety
But Mr Somchai says he is a democratically elected leader and refused to stand down.
He has vowed to act to end the protests but has not set a deadline for doing so.
"The government does not want to trigger any violence or casualties, so to implement the law under international practice, as of now negotiations are under way," he told reporters in the northern city of Chiang Mai.
His plane landed in Chiang Mai earlier this week after the protests meant he was unable to land in Bangkok following an overseas visit.
The government has said that for his own safety, Mr Somchai will remain in the north of the country for the near future.
The protesters have occupied both Suvarnabhumi international airport and Bangkok's Don Mueang airport for three days.
"We are not afraid. We will fight to the death, we will not surrender and we are ready," one leader, Somsak Kosaisuk, told supporters at Don Mueang airport on Friday.
"If they crack down on us we will come back with more protesters."
September 2006: Prime Minister Thaksin Shinawatra ousted in military coup
February 2008: Samak Sundaravej sworn in as prime minister
September 2008: Protesters call for Mr Samak's resignation, saying he is a proxy for Thaksin
9 September 2008: Mr Samak dismissed for violating conflict of interest law. Somchai Wongsawat, Thaksin's brother-in-law, becomes prime minister.
October 2008: Thaksin given a two-year jail sentence for corruption in his absence
On Thursday Mr Somchai said police would be assisted by some military units to end the protests.
Correspondents at the airport say baton-wielding protesters have been handing out goggles and helmets and setting up first aid stations in anticipation of a raid.
Hours after Mr Somchai's statement, government spokesman Nattawut Sai-Kau said police had been told to remove the protesters "as soon as possible" in a "peaceful manner", the Associated Press news agency reported.
"Firstly, the police should open negotiation with the protester. If they refuse to go, police should do whatever is necessary to open the airports on the basis of non-violence," he said.
Lieutenant General Suchart Muenkaew, chief police negotiator at the airport, told reporters he would keep talking to the protesters but that "if it fails we will take other steps".
"The last step will be to disperse them," he said.
The PAD have occupied a government complex in Bangkok for months, and declared at the beginning of this week that they were embarking on the "final battle" of their campaign to unseat the government.
Correspondents say the airport protesters appear increasingly isolated and are losing the support of their traditional sympathisers, the business elite.
The airport closure will cost the country around $4bn (£2.6bn) in lost business and cause serious damage to its reputation as a tourist destination, something which will take the country years to recover from, say analysts.
Thailand has been in political turmoil since former Prime Minister Thaksin Shinawatra was ousted in a military coup in 2006.
The PAD - a loose alliance of royalists, businessmen and the urban middle class - claim that the government is corrupt and hostile to the monarchy.
They also accuse it of being a proxy for Mr Thaksin, who remains very popular among Thailand's rural poor.