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.

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.