The number of people affected by this month's flooding in Sudan has climbed to around 150,000 and is expected to rise further, the United Nations said on Monday.

More than half the victims, 84,000, are in the area around the capital Khartoum, said the UN's Office for the Coordination of Humanitarian Affairs (OCHA).

Twenty people have died in the capital region, the official SUNA news agency reported late Monday, citing Khartoum state authorities who added that 240 people had been hurt.

"More rains are expected in the coming days and the estimated number of affected people is likely to rise further as rains continue and as more information becomes available," OCHA said in a press release.

OCHA's latest estimate follows heavy downpours on Friday night and is based on information from the Sudanese Red Crescent Society and other agencies.

Heavy rains and flash floods began on August 1, initially affecting almost 100,000 people in several states.

At least 26,000 houses have been damaged or destroyed, according to initial estimates cited by OCHA.

Official Radio Omdurman reported on Sunday that the flooding killed 36 people in Nile state north of the capital.

The UN and other agencies have provided aid including tents, plastic sheeting and drinking water, OCHA said.

A volunteer youth group, Nafeer, said on Monday it had found 150 families "trapped" in the Al-Nizeila area on Khartoum's outskirts.

It added that many people who lost their homes are now sleeping outdoors.

This year's flooding is the worst in the capital region in years but water surges in rural areas of Sudan between June and October last year affected about 270,000 people and damaged more than 36,000 homes, according to figures cited by the UN.