Thailand’s prime minister on Tuesday called flooding in the south that has displaced thousands of people “one of the worst natural calamities” to hit the country. Bangkok’s only aircraft carrier, which rarely leaves its berth, was deployed to help out.

Prime Minister Abhisit Vejjajiva spoke after inspecting the battered region from a military aircraft.

A tropical depression that dumped constant rain on the area on Sunday and Monday triggered the flooding, which caused the suspension of some rail services to the south and the temporary closure of the airport on Samui island, a popular tourist getaway in the Gulf of Thailand. Severe flooding has also caused mass evacuations just over the border in Malaysia.

The flooding in Thailand’s south, along a peninsula it shares with Malaysia, follows two weeks of heavy floods in October, mostly in Thailand’s north, that killed 104 people. Nearly six million residents of 38 provinces were affected by the October floods, according to the government’s Disaster Prevention and Mitigation Department.

Mr. Abhisit earlier said that flooding was caused by heavy rains that dumped larger—than—normal amounts of water into dams and reservoirs and aggressive housing and business development that has affected natural drainage channels.

The new flooding has caused a dilemma of whether to evacuate people or try to bring supplies to where they are stranded.

An Islamic boarding school in Hat Yai in the south was forced to evacuate about 450 students and 50 teachers just one day after the semester opened. Students had to be transferred by two motorboats from the school to military trucks one kilometer (0.6 mile) away, school principal Yusuf Nima said by phone.

“At first we thought it would be easier for the over 400 students to stay at their dormitories and get help from the outside world instead of moving out, but we were wrong,” the principal said. “It has proven to be very difficult getting access from anywhere else as the water level hasn’t really gone down.”

The navy sent the aircraft carrier Chakri Naruebet to Songkhla province on a flood relief mission set to begin on Wednesday morning. The vessel will use its helicopters to transport supplies and also serve as a food depot and floating hospital.

Meanwhile, in Malaysia, thousands fled their homes and several schools closed in two northern states that border Thailand.

An official at the flood monitoring centre in Kedah state said more than 7,800 people were staying in shelters on Tuesday after heavy rains caused several rivers in the state to swell to dangerous levels.

Another official with the National Flood Monitoring Centre said more than 2,200 people in Perlis state were evacuated. Both officials declined to be named because they are not authorized to make public statements.

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