Suspected Boko Haram fighters attacked the city of Maiduguri in what has been described as the Islamist militant group's most serious assault on Borno State in a year and a half.
There are no reports of casualties yet.
Aid workers and Reuters witnesses reported explosions and heavy gunfire for at least forty five minutes in the South eastern and South western outskirts of the city.
One report says fighter jets roared overhead as soldiers and police sped towards the scene.
Military authorities released a statement saying the situation is under control and urged the city's inhabitants not to panic.