Clogged flights and tight immigration space were to blame for an hours-long wait for foreigners to come out of Don Mueang in the early hours of Saturday, airport general manager Suteerawat Suwnnawat said.
Only 21 regular flights are scheduled to land at the airport between midnight and 5am every day but Don Mueang was overloaded with four extra flights during that period on Saturday, the airport chief said on Don Mueang's Facebook account.
Two delayed flights from Singapore, one flight from Hong Kong that landed behind schedule and a charter flight from China left hundreds of visitors jammed together in the terminal, enduring lengthy delays as they waited to clear immigration, he added.
Foreigners had to wait more than four hours to have their passports stamped by immigration police on Saturday. Foreign visitors took to social media to vent their anger and frustration over the long queues. (Continues below)
The foreign wife of Piyabutr Saengkanokkul, a law lecturer at Thammasat Universtiy, was among passengers lining up for passport control. She entered the queue at midnight and had her passport stamped four hours and 20 minutes later.
Almost 5,000 incoming passengers were at the airport during the period, the airport said, without elaborating on how many of them were foreign nationals.
Thais escaped the long queues by clearing passport control via automatic gates.
Gp Capt Sutheerawat said immigration authorities can handle only 1,000 visiting passengers in an hour.
The airport was seeking approval from the Civil Aviation Authority of Thailand to expand the immigration area and counters for arriving passengers, he said.
The plan is expected to be completed next month, and would increase immigration capacity to 1,800 passengers per hour, he added.
Don Mueang is a gateway for low-cost airlines to Thailand, a country that is banking on tourism to revitalise its economy.