Damian Chukwu, police commissioner for Borno state, said the attack took place at a fish market around 20 kilometres (12 miles) from the centre of Maiduguri at about 8:00 p.m. (1900 GMT) on Friday.
Chukwu said that a male and two female suicide bombers detonated themselves at the Kasuwar Kifi in Konduga.
Borno state is the part of Nigeria that is worst hit by the Boko Haram attacks.
Idrissa Bana, an eye witness, was quoted as saying that the three bombers simultaneously detonated the improvised explosive devices (IEDs) on their bodies in the crowded market.
Babakura Kolo and Musa Ari, from the Civilian Joint Task Force (CJTF) helping Nigeria's army against Boko Haram, said the bombers were all men.
Two attacked a fish market and a third struck nearby, security sources said.
More than 25 people were injured in the deadly attack, according to local media reports. "The Tashan Kifi is an informal market which serves as an eatery, market and also hang-out for residents".
No group has yet to claim responsibility, though the Boko Haram militant group has stepped up its campaign of suicide bombing using girls, usually veiled, to blow up targets in Nigeria's northeast.
The blasts happened shortly after another bomber killed four and injured 44 at a displaced persons' camp in Dalori, 22 kilometres away on the same road to Maiduguri.
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