The number of people affected by large-scale flooding in South Sudan has doubled to almost a million since September, the UN's emergency response agency has warned.

Estimates by the Office for the Coordination of Humanitarian Affairs (OCHA) say some 909,000 people are suffering in the country of 11 million.

As torrential rains ravage crops and destroy homes, the UN estimates that 71 percent of the population is in need of humanitarian assistance.

South Sudan has endured four consecutive years of flooding, with OCHA warning the disaster now affecting nine out of 10 states.

Widespread damage

The floods have reportedly killed livestock and destroyed crops, washed away roads and bridges, destroyed homes, schools and health facilities, and submerged boreholes and latrines, contaminating water sources and posing risks of waterborne diseases.

In oil-rich Unity state - one of the worst-hit regions - rising water levels breached dykes in two places on Sunday, threatening to flood camps for internally displaced people as well as a base for the UN Mission in South Sudan.

"Efforts are ongoing around the clock to repair the areas needed and to monitor any vulnerable areas ahead of further breaches," OCHA said.

In the west, in Bahr el-Ghazal, torrential rains caused the collapse of a key bridge, cutting off the delivery of emergency aid to already hard-pressed populations.

Since achieving independence from Sudan in 2011, the young nation has been in the throes of a chronic economic and political crisis, and is struggling to recover from the aftermath of a five-year civil war that left nearly 400,000 people dead.

Four out of five of South Sudan's 11 million people live in "absolute poverty," according to World Bank figures for 2018, and nearly two-thirds of its population suffer from severe hunger.

(with wires)