Thai Prime Minister Prayuth Chan-ocha visited flooded parts of the south of the country on Friday where unseasonable downpours have killed six people, cut road and rail links and forced an airport to close.

Thailand's wet season usually ends in late November and heavy rain and flooding is rare in January, which is high season for beach resorts in the south.

Twenty-six flights to and from the main airport in the southern province of Nakhon Si Thammarat airport were cancelled on Friday because the runway was flooded, the Department of Airports said.

"The floods began on January 1 and are due to the unseasonable heavy rain," said an officer at the National Disaster Warning Center who declined to be identified as she is not authorised to speak to the media.

Six people had been killed in accidents caused by the flooding, she said.

Railway services on the main line linking Thailand to Malaysia have been suspended because the track is flooded.

Southern Thailand is a major rubber-producing region and the wet weather was having a significant impact on production, said Uthai Sonlucksub, president of the Natural Rubber Council of Thailand.

"Farmers began tapping in December because they had to wait for the rainy season to end but now they have to contend with the floods," Uthai told Reuters.

Flooding in Thailand usually occurs during the May-November rainy season.

Widespread floods in 2011 killed more than 900 people and caused major disruption to industry, cutting economic growth that year to just 0.1 percent.