Bangkok's main airport resumed full operations Friday in time for the king's birthday after crippling protests, but Thailand's political uncertainty deepened after the monarch cancelled his annual 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 ceremony due mid-morning was to officially reopen Suvarnabhumi international airport, after an eight-day siege by anti-government protesters ended Wednesday.

"There are about 550 scheduled flights due to operate (Friday) at Suvarnabhumi," an Airports of Thailand spokeswoman said, adding that passengers would be treated to puppet shows and dance performances.

"We are confident that all 110 airlines will return to serve 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 their blockade of Suvarnabhumi and the smaller Don Mueang airport 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 at home.

They took their campaign to previously unseen heights on November 25, when thousands of PAD supporters seized Suvarnabhumi, stranding an estimated 350,000 travellers and costing Thailand billions of dollars in lost revenue.

Analysts say there is now a pause in the turmoil as Thais celebrate the king's birthday with reverential ceremonies, but warn that protests could erupt again when the new prime minister is selected.

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 a parliamentary session early next week during which MPs would have voted for a new premier has been cancelled, and no date has yet been rescheduled.

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

"Any effort to nominate another proxy of deposed prime minister Thaksin Shinawatra to lead a new administration will only result in another crisis," an editorial in the Bangkok Post said Friday.

King Bhumibol -- who is the world's longest reigning monarch -- pulled out of the highly anticipated address to the nation at the last minute on Thursday as millions of Thais tuned in their radios.

"His Majesty the King is mildly sick," Crown Prince Maha Vajiralongkorn said in a brief broadcast as 20,000 people waited at Chitralada Villa, the king's official residence in Bangkok.

Princess Maha Chakri Sirindhorn, the king's daughter, said in the same broadcast that his condition was "not serious", adding that 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.