At least 10 people were killed on Saturday when a young girl, believed to be just 10-years-old, blew herself up in the north-eastern city of Maiduguri.
The explosion hit the market just after 12pm (11am) when it was filled with shoppers and traders. The market was targetted by two female suicide bombers last year.
Civilian vigilante Ashiru Mustapha said the bomb detonated as the child was being searched at the entrance to the market.
"The girl was about 10-years-old. I doubt much if she actually knew what was strapped to her body," he told AFP.
"In fact, she was searched at the entrance of the market and the metal detector indicated that she was carrying something. But sadly, the explosion went off before she was isolated, killing at least 10 people and injuring many others."
The death toll could be as high as 20, with 18 injured in market attack, according to local police.
Borno State police spokesman Gideon Jubrin told reporters: "Casualty figure: 20 dead and 18 injured, including the female suicide bomber that detonated the improvised explosive device."
An eyewitness, Abubakar Bakura, said: "The blast split the suicide bomber into two and flung one part across the road.
"Among the dead are two vigilantes who were searching the girl. I am pretty sure the bomb was remotely controlled."
A Red Cross official said: "We have so far evacuated 10 bodies to the mortuary at the (Borno) State Specialist Hospital."
"Many people sustained life-threatening injuries," he added.
No group has so far claimed responsibility, but Boko Haram militants have been known to use young girls as human bombs in their mission for an Islamic State.
Boko Haram launched its first female suicide attack in June 2014 in the northern state of Gombe and there have been several bombings since, including four in a week in the city of Kano.
Nigeria's civilian vigilante forces were formed as a reaction against Boko Harum. The Civilian Joint Task Force consists of at least 8,000 volunteers, who arm themselves with machetes, homemade weapons and firearms.