Thousands of stuck travellers finally flew out of Bangkok's main airport Friday as it resumed full operations, but political uncertainty dragged on after the king cancelled his annual birthday speech.

King Bhumibol Adulyadej turned 81 on Friday but pulled out of his customary birthday address the previous day due to illness, ending hopes that he might offer guidance on a way out of the nation's long-running political crisis.

A mid-morning ceremony complete with puppet shows and classical dance officially reopened Suvarnabhumi international airport, after an eight-day siege by anti-government protesters ended on Wednesday.

"Suvarnabhumi has officially resumed operations. All of the staff here are so happy to return to work," an Airports of Thailand spokeswoman said.

The siege of Suvarnabhumi and the smaller Don Mueang domestic airport left an estimated 350,000 travellers stranded in Thailand, and cost the kingdom billions of dollars in lost revenue.

Frustrated holiday-makers have been struggling to get out via a naval base southwest of the capital and a handful of regional airports, but there is a huge backlog of people waiting to fly out of the "Land of Smiles."

Suvarnabhumi can handle 700 flights and 100,000 passengers a day, although the spokeswoman said she expected up to 80,000 travellers and 550 flights to pass through the hub Friday.

Tourists in sunglasses and shorts milled around the futuristic steel-and-glass terminal, where there was little sign that one week ago thousands of protesters were setting up makeshift food stalls and tents.

Chaisak Angkasuwan, director general of the Civil Aviation Department, urged tourists not to worry about the recent turmoil.

"We are 100 percent in terms of security and safety so the airport should be problem free," he told AFP. "All airlines said they will maintain their operations at Suvarnabhumi."

Dozens of flights had already left the two-year-old hub since a court dissolution of the ruling party gave demonstrators a face-saving way to leave, but check-in and immigration were not up and running until Friday.

The People's Alliance for Democracy (PAD) decided to abandon its blockade of the airports after Tuesday's Constitutional Court ruling forced premier Somchai Wongsawat from office -- a key demand of their movement.

The PAD launched their campaign in May, accusing the government of acting as a puppet for Thaksin Shinawatra, the premier ousted in a 2006 coup who is living in exile to escape corruption charges.

Analysts said there was a pause in the turmoil as Thais celebrated the king's birthday with reverential ceremonies, but warn that protests could erupt again.

Allies of Somchai have vowed to regroup under new names and simply re-form the government, since they still have a majority.

They are set to name a likely successor on Sunday, although no date has been set for parliament to approve a new premier.

The PAD, which draws its support from the urban elite and elements in the military and palace, has warned that it will resume protests if the new prime minister is too close to Thaksin. Somchai is Thaksin's brother-in-law.

King Bhumibol -- the world's longest reigning monarch -- pulled out of his highly anticipated address to the nation at the last minute on Thursday as millions of Thais were tuning in to hear it.

Crown Prince Maha Vajiralongkorn said that the king was "mildly sick" in a brief broadcast, while Princess Maha Chakri Sirindhorn said he "has a blockage in his throat and has poor appetite."

The announcement prompted speculation that the king did not want to get involved in the turmoil that has rocked Thailand since Thaksin was ousted, and sparked concerns for the health of the monarch, adored as semi-divine here.

David Streckfuss, an American historian of Thailand, told AFP that the public had been looking to both the court and the king's speech to "define the political landscape for the future in some way."

"People were looking for a little more direction and reassurance," he said.