At least 21 people have been killed and eight others are missing after the worst flooding in decades across Malaysia's northeast, police said Wednesday, with almost a quarter of a million people displaced.

They said 14 of the deaths were recorded in the worst-hit state of Kelantan, where some 158,476 people were displaced.

Four people died in Terengganu and three in Pahang state. There are also reports of outbreaks of flu and diarrhoea.

The number forced from their homes in the other affected states -- Pahang, Perak, Terengganu and Johor -- totalled 83,570.

Forecasters Wednesday predicted clear skies for the next three days.

"But we are still in the northeast monsoon period until March. We could expect heavy showers later in the week," a meteorological department official said.

Floodwaters have began to subside in many areas but authorities are bracing for possible disease outbreaks.

Noor Hisham Abdullah, health ministry director-general, said there was no major rise in flood-related diseases at the moment.

"We anticipate that flood victims will come in masses seeking care once the floodwaters start to recede," he said in a Facebook posting.

Rajbans Singh, president of the Malaysian Wellness Society, told AFP that floods can increase the transmission of typhoid fever, cholera, leptospirosis, malaria and dengue.

The government has been criticised for it slow response after many victims were caught stranded in outlying areas without food and clean water.

Prime Minister Najib Razak, who came under fire after being filmed playing golf with US President Barack Obama in Hawaii when the disaster happened, said he was saddened by the flooding.

"I see so much destruction. It is depressing and sad," he said.

Najib is criss-crossing flood-hit areas and coordinating aid activities.

Ee Su Chuong, 42, the owner of an auto repair shop in Kota Bharu in Kelantan, said many people were taking advantage of the sunny day to clean their mud-filled homes after floodwaters receded.

"But they will return to the relief centres to spend the night because they are unable to cook on their own as most provision shops are still closed," he told AFP.

The National Security Council admitted there were delays in its relief efforts, saying this was partly because some of its staff were flood victims.

"Due to the magnitude of the floods, most districts were completely inundated. Our entire district machinery collapsed as they (staff) had become victims themselves," council secretary Mohamed Thajudeen Abdul Wahab was quoted as saying by the Star newspaper.