Suspected Boko Haram militants attacked Nigeria's northern city of Maiduguri in Borno state on Wednesday from a cashew plantation a few kilometres from the Giwa barracks, military sources said.
Residents said they heard heavy shooting and explosions on the outskirts and began fleeing their homes.
"I'm trapped near the University of Maiduguri now," local resident Kabir Olaoye told Reuters by phone. The shooting began around 6:45 p.m. (1745 GMT), he said.
The city of around two million people is the birthplace of the jihadi group, which has killed thousands in its attempt to carve out an Islamist state in the country's northeast.
Maiduguri has not experienced an attack since two major takeover attempts in late January and early February and several bombings in March.
Boko Haram claimed an area larger than Belgium last year and was fast becoming a regional threat after it increased cross-border incursions.
Chadian and Nigerian troops entered the fray earlier this year and drove the militants out of some key Borno towns while Cameroonian forces repelled them from its border areas.
The Nigerian military now has the group on the run after launching a ground offensive on their last stronghold in the Sambisa forest reserve at the end of April.
