Health volunteers in Malaysia have been preparing for any surge in waterborne diseases following devastating floods that saw tens of thousands of people evacuated, with concerns in the country that days of constant rain could be on the way.

Floodwaters have begun receding in the worst-hit state of Kelantan, on Malaysia's northeastern coast, but government data showed more than 40,000 people remained at temporary shelters on Wednesday (December 4) amid fears of a potential second wave of flooding this week.

Videos of children playing in muddy flood waters have gone viral online in recent days, sparking concerns over the potential spread of waterborne illnesses.

Nearly 5,000 cases of infectious diseases - including stomach flu and respiratory and skin infections - have been detected at Kelantan relief centres so far, government news agency Bernama reported on Tuesday (December 3), citing state health authorities.

READ: Floods displace 122,000 people in Malaysia

The Malaysian Medical Relief Society, or MERCY Malaysia, said the number of reported cases have been manageable but its volunteers remained on alert for any future spikes.

The Meteorological Department on Wednesday (December 4) said it expected a monsoon surge from December 8 to 14, which could bring continuous rain to the east coast of Malaysia's peninsular and parts of Sabah and Sarawak states on Borneo island.

(Production: Mandy Leong Huey Mun, Joe Raggett)