Protesters trying to overthrow Thailand's government have attacked Bangkok's police headquarters as demonstrations against the Prime Minister, Samak Sundaravej, spread from the capital and disrupted air and rail services.
Police fired what appeared to be tear gas at the 2,000-strong crowd, taking part in escalating protests that have raised fears of major violence and military intervention less than two years after a coup in September 2006.
Protesters also forced airports to close in the tourist destinations of Phuket and Krabi and the southern town of Hat Yai, leaving hundreds of passengers stranded.
Striking rail workers halted 30 per cent of services nationwide, and airline and port workers were urged by their union leaders to take sick leave.
In Bangkok, where protesters have occupied the prime minister's compound since Tuesday, some of Mr Samak's advisers urged him to impose emergency rule, according to two government sources.
"It has been proposed as an option to him," said one source, who declined to be named.
But Mr Samak, who leads a coalition government elected in December, declined to get tough with the People's Alliance for Democracy (PAD), which began its protest campaign on 25 May.
"I have several tools at my disposal, but I am not using any of them because I want to keep things calm," he told reporters after meeting top military and police officers.
"I will not quit. If you want me out, do it by law, not by force. This is embarrassing in front of the world."
Imposing a state of emergency would allow the government to deploy soldiers to disperse the protesters, although the army chief Anupong Paochinda said the situation did not warrant it.
"It will hurt the country's image and worsen the country's situation," he said, nearly two years after the coup that removed the prime minister Thaksin Shinawatra but failed to heal the deep divisions in Thai society.
Thai shares have fallen 23 per cent since the street campaign began in May amid fears of policy paralysis at a time of stuttering economic growth and bloodshed on the streets.
The protesters' assault on police headquarters came hours after riot officers tried to deliver an eviction order and clashed with demonstrators barricaded inside the compound. "We are trying to deal with the protesters as gently as possible," said a police spokesman, Surapol Thuanthong.
After the scuffles, the Civil Court said that it had retracted its earlier eviction order after the demonstrators appealed against the ruling.
The People's Alliance for Democracy, a group of businessmen, academics and activists whose 2005 protests against Mr Thaksin contributed to the coup against him, have accused Mr Samak of being an illegitimate proxy of the former prime minister, who is now living in exile in London. Mr Samak has denied the accusation.
"Today is the Judgement Day. It is the People's Revolution and we must win," said the alliance leader Sondhi Limthongkul after raids on government offices and a state TV station on Monday.
Mr Sondhi is one of nine PAD leaders charged with insurrection, a crime that can carry the death penalty.
The alliance also proclaims itself to be a defender of the revered King Bhumibol Adul-yadej against an alleged Thaksin plan to turn Thailand into a republic – a charge vehemently denied by both Mr Thaksin and the government.
The protesters have barricaded themselves in the 11-acre compound behind razor wire and car tyres. Sentries armed with bars and golf clubs poured a mixture of gasoline and shampoo across the road, turning it into an ice-rink.
At the barricades, alliance supporters held aloft pictures of King Bhumibol, shouting "We love the King. We love Thailand". Inside the compound, thousands sat on plastic sheeting, clapping and cheering speeches by the group's leaders.