Floods in Kelantan worsened after a dam burst in southern Thailand as the nationwide death toll rose to 23.

Deputy prime minister Najib Razak said water levels at the Golok river, which marks the boundary between Malaysia and Thailand, rose above the danger level of nine metres to 10.51 metres.

"I was told the broken dam has caused a higher volume of water to enter Golok river and move towards Rantau Panjang and other adjacent areas," Najib was quoted saying on The Star newspaper's website.

The official Bernama news agency reported that among the latest victims was a six-year-old girl who fell into flood waters while playing in the backyard of her family home in Kelantan.

It reported the number of flood evacuees in Kelantan rose sharply to 6,039 on Monday from 3,772 the previous day, while in Pahang 21,699 were being housed in relief centres.

But in Johor, flood conditions improved steadily, with 3,500 people remaining in relief centres after the weekend, compared with almost 5,000 last week.