Witnesses say a bomb has exploded outside the state secretariat offices in a bustling downtown area of Nigeria's northeastern city of Maiduguri.

Ambulances with blaring sirens have rushed to the scene and soldiers have cordoned off the area.

Residents blamed Boko Haram Islamic extremists though it was impossible to immediately verify the cause of the explosion.

It comes the day after worshippers prevented a suicide bomber from entering a mosque on the outskirts of Maiduguri, the birthplace of Boko Haram and headquarters of the Nigerian military's campaign against the jihadists. The military said the bomber blew himself up and wounded four people.

Thursday's bombing would be the first successful attack in more than two months. Soldiers and civilian self-defense groups have reported preventing several suicide bombings in recent weeks.