"It seems more than 50 have been killed, but less than 75. There are more than 20 injured in the hospitals," he said, adding these numbers could rise.

Ali said these were the worst floods he had seen in Sudan. "One man who was about 90 years old told me he had never seen waters like these in his entire life," Ali added.

He said 18,000 houses had been affected.

The International Federation of Red Cross and Red Crescent Societies said in a statement from Geneva the floods could affect some 2.4 million people across 16 of Sudan's 26 states.

"With the season expected to run until mid-October, meteorological organisations in the region are predicting that as many as 2.4 million people across 16 states could be affected, with areas in the north and east expected to bear the brunt of the damage," the Federation said.

It appealed for 2.1 million Swiss francs (US$1.75 million) to help some 40,000 Sudanese whose homes have been destroyed in flash floods.

Rains, flash floods and overflowing rivers forced hundreds of families to seek main roads, often the highest ground around, as they watched houses and possessions get washed away.

Sudan's Ali blamed climate change and countries who have been polluting the environment for worsening rains.

Aid workers have said with better monitoring and planning Sudan's authorities could prevent deaths.

The civil defence authority said people build in high-risk areas close to river banks or in flood-prone plains, ignoring government warnings.

Rainy season from around June to September each year in Sudan causes floods, especially in the east. Sudan is mostly desert at other times of the year and uses little of the river Nile waters allocated to it under an east African treaty for agriculture.

Levels of the Nile in Khartoum last year were higher than in 1988 and 1946 when the worst floods of last century hit Sudan. Last year some 10,000 houses were destroyed during about four months of rains.