The blast happened at about 11:00 am (local time) yesterday at the weekly market in Wagir, in the Gujba district south of the Yobe state capital Damaturu.
"It was a suicide attack by a girl of around 12 years," Hussaini Aisami, whose relative was among at least 30 people injured by the blast, told AFP.
"She went into the market and headed straight to the grain section. She detonated her explosives in the middle of traders and customers. Ten people died from the explosion. We brought 30 people to the hospital."
On Monday, a girl thought to be aged about 17 killed at least 20 at a bus station near a fish market in the Borno state capital, Maiduguri, when the explosives she was carrying went off.
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A girl about the same age was also killed nearby when she blew up but there were no other casualties.
Security analysts studying the phenomenon have suggested that younger girls may have their explosives detonated remotely by a third party.
The latest deaths are another reminder of the threat posed by Boko Haram, despite the group being pushed out of captured territory by a four-nation military offensive since February.
Suicide attacks, raids and shelling have increased since new President Muhammadu Buhari took power on May 29 vowing to crush the militants.
In all, some 208 people have been killed since then, according to AFP reporting.