At least 47 students have been killed by a suicide bomber at a school assembly in the north-east Nigerian town of Potiskum, police have said.

The explosion happened at a boys’ science and technical school in the town.

Militant group Boko Haram is believed to have caused the blast, police said.

It has often targeted schools during its five-year campaign to establish an Islamic state, which has left thousands dead.

A suicide bomber disguised in a school uniform caused the explosion, survivors are quoted by Associated Press news agency as saying.

“We have 47 dead and 79 injured,” police spokesman Emmanuel Ojukwu told AFP.

The school was a mass of abandoned footwear and blood, resident Adamu Alkassim said.

“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 is quoted by AFP as saying.

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 their children's bodies at the hospital.

The blast underlines the lack of security in north-eastern Nigeria, says BBC Nigeria correspondent Will Ross.

Boko Haram, whose names means Western education is forbidden, is waging a sustained campaign to prevent children from going to school.

It believes girls should not attend school and boys should only receive an Islamic education.

In April, the group sparked global outrage by abducting more than 200 girls from a boarding school in Chibok town in Borno State.

It says the children have converted to Islam, are learning to memorise the Koran and have been married off.

Potiskum in Yobe State has often been targeted by Boko Haram.

Last week, a suicide bombing killed 15 people in the town.

The bomber joined a religious procession of the rival Shia Muslim sect, before blowing himself up.

Update news