The number of internally displaced people has been rising since fighting started on Dec 15 in the capital, Juba, before spreading across the oil-producing East African nation.
Aid agencies now need at least $166 million to save lives, according to the UN, which has urged South Sudan's leaders to start talks.
Regional leaders under a bloc called IGAD are meeting today in the Kenyan capital of Nairobi to discuss the crisis in South Sudan. That meeting is expected to produce a roadmap for peace talks between South Sudanese President Salva Kiir and the political rival he accuses of mounting a failed coup.