BANGKOK — Advancing Thai floodwaters breached barriers protecting Bangkok's second-largest airport on Tuesday, halting commercial flights, as the prime minister warned that the capital could be swamped by up to 5 feet (1.5 meters) of water if flood walls fail.
The flooding at Don Muang Airport, which is primarily used for domestic flights, is one of the biggest blows yet to government efforts to prevent the sprawling capital from being inundated. Its effective closure is certain to further erode public confidence in the ability of Prime Minister Yingluck Shinawatra's administration to defend the increasingly anxious metropolis of 9 million people.
Bangkok's Suvarnabhumi Airport, the country's main international gateway, has yet to be affected by flooding and flights there were operating normally. Most of the city has been spared inundation so far.
Yingluck's government declared a five-day public holiday on Tuesday in affected areas, including Bangkok, while the Education Ministry ordered schools to close until Nov. 7.
The prime minister warned in a televised address that in a worst-case scenario, the enormous pressure of floodwaters pushing downstream into the city could combine with monthly high tides this coming Friday and Saturday to overwhelm recently reinforced flood walls and embankments protecting the city.
That could result in flooding of up to 5 feet (1.5 meters) in low-lying areas of the capital, she said.
Bangkok Gov. Suhumbhand Paribatra said the capital cannot escape flooding and warned residents of 13 districts along the Chao Phraya river, the city's biggest waterway, to be prepared.
The flooding Tuesday at Don Muang airport symbolizes the gravity of the Southeast Asian nation's deepening crisis, which has seen advancing waters drown a third of the country and kill 366 people over the last three months.
The airport houses the government's recently established emergency Flood Relief Operations Center, and one of its terminals has been converted into an overcrowded shelter filled with tents for about 4,000 people who fled waterlogged homes.
Somboon Klinchanhom, a 43-year-old civil servant who took refuge there last week, was preparing to move after authorities said the terminal had become too crowded and thousands of people displaced there would be relocated.
"I thought it would be safe and well-protected," Somboon said of the airport, as she packed her belongings again.
Though floodwaters have yet to spill across Don Muang's runways, ankle-high water could be seen Tuesday rushing over sandbagged barriers around the airport's perimeter, swamping internal roads. One vast pool was headed toward two jetliners parked outside a hangar, their wheels wrapped in plastic sheets.
Capt. Kantpat Mangalasiri, the airport's director, said Don Muang's commercial runways would be closed until Nov. 1 to ensure safe aircraft operations.
Thai air force relief flights were continuing on a military runway that is still open, air force spokesman Montol Suchukorn said. He said floodwaters had breached the military's air base, but the runway remains protected by flood barriers.
Last week, the air force moved 20 planes from Don Muang as a precaution.
The government's flood relief command will remain at the airport for now since it is still accessible by road, spokesman Wim Rungwattanajinda said.
The scene at the domestic terminal was chaotic as throngs of confused passengers struggled to leave or pulled up to the departure hall with luggage, unaware their flights had been canceled. Some travelers waited hours for a ride as airlines scrambled to arrange special buses.
Last week, Yingluck ordered key floodgates opened to help drain runoff through urban canals to the sea, but there is great concern that rising tides in the Gulf of Thailand this weekend could slow critical outflows and flood the city.
Late Monday, the flood relief center said water levels in the worst-hit parts of the country — the submerged provinces north of Bangkok — were stable or subsiding. But the massive runoff was still bearing down on the capital as it flowed south toward the Gulf of Thailand.
While neighborhoods just across Bangkok's boundaries are underwater, most of the city is dry and has not been directly affected by the deluge.
Anxious Bangkokians, though, have been raiding stores to stock up on emergency supplies, and many have been protecting their homes and businesses with sandbags. Some have even erected sealed cement barriers across shop fronts.
• Associated Press writer Vee Intarakratug contributed to this report.