Floods in southern Thailand have killed at least six people and affected tens of thousands of households, authorities said on Wednesday.

The floods, which began on 22 December, have hit more than 70,000 homes across the provinces of Satun, Songkhla, Pattani, Yala and Narathiwat, regional officials said.

Six people including an 89-year-old woman and a toddler were killed in Narathiwat, deputy provincial governor Preecha Nualnoi told AFP.

Another person was still missing following days of intense rain, which sparked floodwaters that reached around three metres in height in some places, he said. 

Local media footage showed streets submerged by the muddy deluge and residents taking refuge on rooftops. 

Relief teams worked by night to hand out bottled water and snacks and check buildings for damage or casualties. 

Thailand's Department of Disaster Prevention and Mitigation said the water level had reduced on Wednesday morning.

Some rail services in Narathiwat province, which borders Malaysia, had resumed following days of closure due to track subsidence, deputy governor Preecha said. 

The kingdom's rainy season typically brings months of daily deluges but scientists say man-made climate change can make rainfall more intense.

In 2011, widespread flooding killed hundreds and damaged millions of homes around the country.