A bomb blast has killed at least 48 students after striking a school assembly in the north-eastern Nigerian state of Yobe, according to a morgue worker.

"The students had gathered for the morning assembly when something exploded in their midst with a thunderous sound at exactly 0750am [0650 GMT]," a teacher at the school told AFP news agency.

Local media also reported that the explosion, at a boys' science and technical school in the town of Potiskum, caused scores of casualties.

No group has yet claimed responsibility for the attack, but suspicion is likely to fall on Islamist militant group Boko Haram as they continue to wage an insurgency on Nigeria's north-eastern regions.

Boko Haram stands for "Western education is forbidden" and the group have continuously carried out attacks to prevent children attending school. In April, the group sparked international condemnation after kidnapping over 200 schoolgirls from a boarding school in the village of Chibok.

The state of Yobe has been placed under a state of emergency as well as the states of Borno and Adamawa because of the group's campaign of terror.

The group has routinely targeted schools in its campaign to establish an Islamic "caliphate" in north-eastern Nigeria.

According to Human Rights Watch, the militants have killed at least 2,053 people since the beginning of 2014, but researchers at the John Hopkins University School of International Studies estimate that 7,000 people have been killed in the 12 months between July 2013 and June this year.

Last week, the group killed at least nine people in a suicide bomb attack on a bank in the town of Azare in Bauchi state.