Malawi (AFP) - Malawi deployed military helicopters and boats Thursday in a bid to rescue desperate flood victims stranded on patches of high ground after raging waters killed at least 48 people and left 100,000 homeless.

"Around 800 people people have been rescued from the flooded areas in (the southern districts of) Nsanje and Chikwawa," Vice President Saulos Chilima said in a statement.

Chilima said the operation had been delayed because of poor weather over the two previous days and helicopters were struggling to land because of the high water levels.

"We need more support such as boats, helicopters, tents and food for the 100,000 affected people," he said.

The two districts were the worst hit by floods ravaging half of the 28 districts in the southern African nation, which is among the world's poorest.

"We are racing against time to rescue everybody. We want to make sure everybody is safe," Chikwawa district commissioner Alex Mdoko told AFP.

Scores of people in the district were feared dead after they were swept away by the floods, he said.

But it was not possible to say how many were missing "until we count everybody and our operation is successful".

Five major roads in the south have been closed after bridges were washed away, including some on the road to the prime tourist destination of Mangochi on the shores of Lake Malawi.

President Peter Mutharika has called the floods a "national tragedy that urgently needs both local and international response."