Aid agencies have said that the world's youngest country, highly vulnerable to climate change, is in the grip of its worst flooding in decades, mainly in the north.

The UN Office for the Coordination of Humanitarian Affairs (OCHA) said about 1.4 million people were affected by floods in 43 counties and the disputed Abyei region, which is claimed by both South Sudan and Sudan.

"Over 379,000 individuals are displaced in 22 counties and Abyei," it added in a statement issued late on Friday.

A surge in malaria has been reported in several states, it said, "overwhelming the health system and exacerbating the situation and impact in flood-hit areas".