The death toll from a devastating landslide in southern Ethiopia has risen to 257, the United Nations said Thursday, warning it could increase to up to 500.

The disaster occurred on Monday following heavy rains in a tiny community in a mountainous area of South Ethiopia regional state. The last toll, given by the local authority on Tuesday, was 229.

"The death toll has risen to 257," as of July 24, the UN's humanitarian agency OCHA said in statement on Thursday, citing local authorities.

"The death toll is expected to rise to up to 500 people," it said.

15,000 need to evacuate

At the scene in Kencho Shacha Gozdi, hundreds of people combed through the sodden red mud as they searched for survivors of the deadliest landslide recorded in Africa's second most populous country.

"More than 15,000 affected people need to be evacuated," OCHA said, including at least 1,320 children, as well as 5,293 pregnant women and new mothers.

South Ethiopia has been battered by the short seasonal rains between April and early May that have caused flooding and mass displacement, according to OCHA.