About 150 riot policemen fled their checkpoint on the highway leading to the airport as the protesters burst from the vehicles, tossed firecrackers and attacked them with iron bars, wooden staves and slingshots.
The charge by members of the People's Alliance for Democracy (PAD) lasted under a minute. When it was over, the highway was littered with discarded police helmets and truncheons.
The five-lane highway was the main access route to the besieged international airport. The policemen had orders not to retaliate against members of the PAD, who have occupied the Suvarna-
bhumi and Don Muang airports in their months-long campaign to topple the Somchai government.
Earlier, another breach in the police cordon was made when a large group of protesters forced riot policemen to abandon a separate checkpoint. There was no violence, but one officer was reportedly detained by PAD 'security guards'.
The assaults on the police come amid rising tensions.
The PAD, which accuses the government of being corrupt proxies of ousted premier Thaksin Shinawatra, is refusing to budge from Suvarnabhumi, where up to 2,000 policemen are assembled around the sprawling complex.
The government's patience appears to be wearing thin with the PAD crowd who took over the two airports.
One warning has already been issued for the PAD supporters to leave.
'The police will issue another warning to protesters to leave the two airports. The language in this warning will be stronger than the first one,' said Major-General Amnuay Nimmano, a police spokesman.
If they still do not leave, a deadline will be issued 'in the third warning - the last one before we take action', he said.
Yet the number of protesters in Suvarnabhumi continued to swell yesterday, with the ferrying in of supplies for the thousands already gathered there.
The government's warnings to the PAD, to disperse or face action to clear them, were scoffed at by the movement's leaders. An offer by Prime Minister Somchai Wongsawat to negotiate without preconditions was likewise rejected.
Trade unionist Somsak Kosaisuk, a co-leader of the PAD, said the movement would not agree to talks with the Prime Minister unless he resigned.
'If they come, we'll not open the door. If they shoot us, we'll shoot them back. We'll die if that makes the country better,' said another PAD leader Sondhi Limthongkul.
As the crisis dragged on, analysts pointed to two landmark events this week which could be turning points in the protracted power struggle.
The first is a case against the ruling People Power Party (PPP), seeking its dissolution on grounds of electoral fraud. Most expect the court to rule for dissolution in the verdict due on Tuesday.
Dissolution raises the possibility of Mr Somchai no longer being Prime Minister by mid-week, and will open a new set of options, including that of an interim caretaker administration.
The second event is the annual birthday-eve speech of King Bhumibol Adulyadej, due on Thursday evening.
Some strategists in the ruling PPP believe that, given the police wariness and army reluctance to crack down on the PAD, the King will have to step in to prevent greater damage from being done to the country.
International pressure is mounting, with the United States government and the European Union yesterday issuing statements of concern at the seizure of the airports.
Many analysts therefore see this week as a possible turning point in the immediate crisis - but remain sceptical over whether deeper issues fuelling the power play will be resolved.
Meanwhile, with the Premier in Chiang Mai, more analysts are talking of a virtual split in the country.
'We have two seats of government now,' Chulalongkorn University political scientist Thitinan Pongsudhirak said. 'One (Bangkok) has been forfeited to the PAD; the other is being assumed in Chiang Mai.'
The Premier, however, must visit Bangkok on Thursday to appear before the King to hear his birthday address at a customary ceremonial audience with the entire Cabinet and senior civil servants.