At least 22 Sudanese children drowned on Wednesday when their boat sank in the Nile while they were on their way to school, official media said.
A woman also died when the vessel went down around 750 kilometres (470 miles) north of the capital Khartoum with more than 40 children on board, the SUNA news agency reported.
"The accident was caused by engine failure halfway across because of a strong current," it said.
The victims' bodies have not yet been found, SUNA added.
Villagers in the region rely on wooden boats to cross the Nile.
A witness told AFP by telephone that the boat had been crossing the river against the current.
"All the families (in the area) are in mourning," added the witness, who did not want to be named.