Thousands of Sudanese need food, water and shelter, a source in an aid organisation said on Tuesday, after they fled a widening rebel offensive that swept through a previously peaceful area.
The source in Sudan's Humanitarian Aid Commission (HAC) told AFP that several thousand from one district alone, Abu Kershola, had converged on the North Kordofan town of El Rahad.
"They are in a miserable situation," said the source, asking for anonymity.
He said a team from HAC is in the area to assess people's needs.
Abu Kershola, in the far north of South Kordofan state, was one of several areas in North and South Kordofan which the Sudan Revolutionary Front (SRF) rebel alliance said it attacked on Saturday.
Villagers from Abu Kershola earlier told AFP they were living rough under trees after fleeing.
The rebels briefly occupied Umm Rawaba, the second-largest town in North Kordofan. Residents complained their community had been left undefended, but government bombers and helicopters were in the air after the attack.
Except for occasional rebel forays over the border from the conflict-plagued Darfur region, North Kordofan had been generally peaceful.
SRF said they attacked as part of their strategy to reach the capital Khartoum and overthrow the 24-year regime of President Omar al-Bashir.