At least 20 students have reportedly been killed by a bomb at a school assembly in the north-east Nigerian town of Potiskum.
The explosion happened at a boys’ science and technical school in the town.
Militant group Boko Haram is likely to be blamed for the attack.
It has often targeted schools during its five-year campaign to establish an Islamic state, which has left thousands dead.
“The students had gathered for the morning assembly when something exploded in their midst with a thunderous sound at exactly 7:50 am [06:50 GMT],” a sobbing teacher told AFP news agency.
Victims were being rushed to a nearby hospital, said the teacher, who asked not to be identified.
A witness told the BBC he saw parents wailing at the sight of the bodies of their children at the hospital.
No group yet claim the attack, but in the past Boko Haram militants had attack schools and killed dozens of students in Yobe state. Yobe is one of the three states under state of emergency as a result of activities of Boko Haram.