Soldiers rushed to the scene in the city of Potiskumbut, the capital of Yobe state, but were chased away by a crowd throwing stones and shouting.
They were angry about the military’s inability to halt a five-year Islamist insurgency that has killed thousands of people and driven hundreds of thousands from their homes.
A suicide bomb attack in the same city killed 30 people a week ago, when suspected Boko Haram fighters attacked a religious procession of moderate Muslims.
Some 2,000 students had gathered for yesterday morning’s weekly assembly at the Government Technical Science College when the explosion blasted through the school hall.
Student Musa Ibrahim Yahaya, 17, said: “We were waiting for the principal to address us, around 7.30am, when we heard a deafening sound and I was blown off my feet. People started screaming and running. I saw blood all over my body.”
She is hospital being treated for head wounds.
Hospital records show 79 students were admitted and health workers said they included serious injuries that might require amputations. The hospital was so overcrowded that some patients were squashed two to a bed.
A mortuary attendant said 48 bodies were brought to the hospital and all appeared to be between the ages of 11 and 20.
Survivors said the bomber appeared to have hidden the explosives in a type of rucksack popular with students.
Months ago, Nigeria’s military reported finding a bomb factory where explosives were being sewn into rucksacks in the northern city of Kano.
Garba Alhaji, father of one of the wounded students, said there was no proper security at the school.
“I strongly blame the Yobe state government for not fencing the college,” he said. He added that just three months ago a bomb was discovered in the school and removed by specialists.
Many Nigerians are angry that Boko Haram has increased attacks and bombings since the government on October 17 claimed to have brokered a ceasefire.
Boko Haram leader Abubakar Shekau has denied negotiating a truce.
No one immediately claimed responsibility for the attack, although local police believe it was carried out by the Nigerian militant group.
Boko Haram released a new video yesterday, showing militants in armoured vehicles driving up and down roads in an unidentified town, reportedly Shekau, which is said to have fallen under their control.
The ceasefire agreement announced by the Nigerian government last month involved the imminent release of more than 200 school girls kidnapped by the group.
But the group’s leader denied a ceasefire deal had been reached, and also said the schoolgirls have not been released.
Boko Haram – which means “western education is sinful” –has attacked schools and killed thousands in its fight for an Islamist state. In April, the group kidnapped nearly 300 girls from their school in the town of Chibok in the north eastern Borno state.