Malaysia and Thailand are facing a second wave of heavy rain and potential flooding this week, authorities said on Monday, even as some displaced residents were able to return home and the worst floods in decades began receding in some areas.

At least 13 people died and tens of thousands evacuated in one of the worst floods in decades to batter southern Thailand and northern Malaysia.

Fourteen provinces in southern Thailand have been warned to prepare for potential flash floods, runoff, and prolonged flooding between Dec 3 to 5.

KUALA LUMPUR/BANGKOK (Reuters) -- Malaysia and Thailand are facing a second wave of heavy rain and potential flooding this week, authorities said on Monday, even as some displaced residents were able to return home and the worst floods in decades began receding in some areas.

There are worries in Malaysia and neighbouring Thailand that disastrous flooding could get worse as more rain comes.

The death toll from the worst floods in decades in southern Thailand and northern Malaysia climbed to at least 12 on Saturday, authorities said, as tens of thousands of people were evacuated due to rising water levels in the past three days.

Floods in northern Malaysia and southern Thailand have claimed the lives of at least 12 people, and 135,000 individuals have been forced to leave their homes. Authorities warn that the number of casualties may increase.