At least six people were killed in a series of bomb blasts in Nigeria's second biggest city Kano on Friday, officials and witnesses said.

One blast gutted the police headquarters for the north of the city, killing at least three people, while another at the passport office also killed three, witnesses said.

At least four other explosions echoed across the city in quick succession, as some residents ran around shouting and screaming. There was no immediate claim of responsibility for the attacks.

(Reporting by Mike Oboh; writing by Tim Cocks; Editing by Jon Boyle)