Days of torrential rain and flooding have killed at least 14 people in southern Thailand, with authorities declaring much of the region a disaster zone, the government said on Tuesday.

Heavy rains have lashed the central part of Thailand's south for much of the last week, including the popular tourist draws of Krabi, Koh Samui and Koh Pha-ngan, affecting some flights and ferry services.

"582,343 people from 88 districts are affected and 14 have people have been killed," the interior ministry said in an update.

Three people have been injured, the statement added, with 11 southern provinces declared disaster zones, a process that frees up more emergency government aid and resources.

At least three people are known to be missing.

In Saiburi district, Pattani province, rescuers on Tuesday were searching a swollen river for two missing boys who were swept away in a flash flood as anxious relatives looked on, an AFP photographer at the scene said.

Railway services have also been suspended south of Nakhon Si Thammarat province after floodwaters covered the train line there.

The rains are unusually heavy for this time of year, with most of Thailand usually experiencing a cooler, dry period from early November -- part of a three month long peak tourist season that is crucial to the economy.

Thailand's Meteorological Department has forecast continued downpours across the region for the next few days.