Thailand's second-busiest airport was closed Friday afternoon after 5,000 protesters set up a blockade and marched down the tarmac, forcing authorities to suspend flights to and from the island.
About 400 protesters from the so-called People's Alliance for Democracy (Pad), which is also squatting on the main government compound in Bangkok, blocked access to the airport Saturday.
Frustrated travellers carrying backpacks and rolling luggage behind them tried to enter the terminal. About 100 made it inside before the protesters started turning them away.
"I want to go home. I have nothing to do with this situation," one frustrated Australian man told AFP.
Wicha Nurnlop, director of Phuket International Airport, told reporters that the airport would remain closed at least through 6pm (1100 GMT) on Saturday.
So far more than 100 flights have been cancelled, including 25 on international routes, leaving 15,000 passengers stranded, Wicha said.
Tourists have been given free hotel rooms until the airport reopens, while authorities were scrambling to arrange buses for about 100 passengers trying to connect to onward flights in Bangkok, he added.
Few police were seen at the airport, and protesters appeared to have been allowed to roam facilities freely.
Wicha said protesters were demanding the government release 85 detained activists and calling for Prime Minister Samak Sundaravej's resignation.
The nearby Krabi airport also remained closed since Friday evening, the operator Airports of Thailand said.
But the southern airport in Hat Yai had reopened for a Thai Airways flight early Saturday, after protesters had forced its closure on Friday as well.