A tourist waits inside Bangkok's Suvarnabhumi international airport after anti-government protesters blocked the main road November 25, 2008. [Kerek Wongsa/REUTERS]
Using trucks and cars, demonstrators also cut off highway access to the airport.
The siege was aimed at Prime Minister Somchai Wongsawat, who is scheduled to return to Thailand on Wednesday from the APEC summit in Peru.
A government spokesman said Somchai will be landing at a military airport to avoid confrontation.
The airport siege followed a clash earlier on Tuesday evening.
Members of the anti-government People's Alliance for Democracy were returning from a rally at the smaller Don Muang airport when government supporters threw rocks at their trucks.
The anti-government group responded by firing slingshots.
Police said 11 people were wounded in Tuesday's fighting, most of them government supporters.
The protest group said the airport will be shut down "until Somchai quits".
The clash was the second time in recent months that the two sides have fought. And it marks the first major violence since October 7, when street battles with police and anti-government forces left two dead and hundreds wounded.
(CCTV November 26, 2008)