An aerial view shows flooding in Hat Yai district of Songkhla province, south of Bangkok, on Tuesday. A tropical depression that dumped two days of constant rain on southern Thailand has caused flooding that forced rail service to shut down and thousands of residents to flee. (Daily News/Associated Press)Thailand's prime minister describes flooding in the country's south that has displaced thousands of people as "one of the worst natural calamities" the country has seen.

The country's only aircraft carrier, which rarely leaves its berth east of Bangkok, was deployed to help out.

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

A tropical depression that dumped constant rain on the area 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 tourist getaway in the Gulf of Thailand.

The flooding in the south follows two weeks of heavy floods in October, mostly in the north, that killed 104 people. Nearly six million residents of 38 provinces in the north, east, central and northeast regions were affected by October's floods, according to the government's Disaster Prevention and Mitigation Department.

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

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

An Islamic boarding school in Hat Yai in the south was forced to close just one day after the semester opened. About 450 students and 50 teachers had to be transferred by two motorboats from the school to military trucks a kilometre away, school principal Yusuf Nima said by phone.

"At first we thought it would be easier for the more than 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 Wednesday morning. The vessel will use its helicopters to transport supplies and also serve as a food depot and floating hospital.