KUALA LUMPUR (REUTERS) - Malaysia's worst flooding in a decade has forced nearly a quarter of a million people from their homes, officials said on Tuesday, with the government coming under renewed fire for its perceived slow response.

The National Security Council said that "exceptionally high" water levels had cut off rescuers from relief centres as the death toll rose to 21 across the northeast. Fifteen people have been killed in neighbouring southern Thailand.

Most criticism was directed at Prime Minister Najib Razak for his absence as the disaster unfolded after being photographed playing golf with President Barack Obama in Hawaii. "No matter how prepared we are, there will always be a bigger and more devastating disaster that tests the capability and resources of the country," the council said in a statement to the online news portal, the Malaysian Insider.

Opposition member Tony Pua denounced the government's reluctance to declare a state of emergency and its "complete lack of urgency" in calling a council meeting. "We are running a headless government with no urgent, cohesive and proactive response to the arising chaos," Mr Pua said in a statement.

Northeastern Malaysia and southern Thailand are hit by flooding during the annual northeast monsoon but this year the rain has been particularly heavy.

Malaysia's eastern states are home to many rice fields but officials have not provided an initial estimate of damage.

Mr Najib on Tuesday visited Kelantan, one of eight flooded states where the water levels have receded to allow many of the major roads to reopen.

Five southern Thai provinces - Narathiwat, Yala, Pattani, Phatthalung and Songkhla - were still flooded. Nearly 10,000 people have been evacuated.