Kano - A suicide bomber targeted students at a technical college in Nigeria's second city of Kano on Wednesday as the campus reopened following a Muslim holiday, witnesses said.
Details on casualties were not immediately known after the sixth attack in the key northern city in the last week, with the violence blamed on Boko Haram members who are waging a brutal five-year insurgency.
The bomber targeted students who had crammed around a notice board to check their assignments for a mandatory government programme known as the National Youth Service Corps (NYSC).
"It was a huge crowd and people were jostling to go through the lists," said witness Isyaku Adamu.
"A huge explosion" by a bomber who was embedded within the crowd caused casualties, he said, but the scene was too chaotic for him to assess any loss of life.
Accounting student Kabir Muazu said he was sitting in a nearby lecture hall when a massive blast rang out.
"We all rushed to find out what it was," and saw the damage of the latest suicide attack in the embattled city, he said.
Kano has been hit by Boko Haram repeatedly through the group's uprising aimed at creating a strict Islamic state in the mainly Muslim country.
But the city saw a clear decline in violence earlier this year, as the insurgents appeared to be concentrating on their stronghold in the remote northeast.
But the militants have since April carried out waves of strikes in major cities across the north and centre of the country, underscoring the grave threat they pose to Nigeria, Africa's most populous country and top oil producer.