The explosion struck at around 1.30 p.m. in the town of Sabon Gari, Borno which is the heartland of the Islamist militant group.
“So far, 52 people are injured, 47 dead persons have been removed from the market,” Umar Kidda, a member of a civilian vigilante group, told Reuters by phone.
Kidda, who witnessed bodies being taken away, said the market was busy when the explosion occurred.
A military source who declined to be named said around 50 people had been killed.
An operative of the Civilian-JTF, Yohana Markus, who claimed to have visited the scene, said “over 50 persons were killed and 45 other traders got injured”.
He said most of the injured were taken to hospital in Biu town.
A hospital source in Biu who would not want to be quoted said “we have admitted 41 injured persons who are currently being given medication, while over 20 other bodies “mostly burnt or battered beyond recognition were also brought to the mortuary”.
Boko Haram has killed thousands of people during a six-year armed campaign to set up an Islamic state in northeastern Nigeria.
According to a Reuters tally, more than 600 people have been killed in raids and bombings by the insurgents since President Muhammadu Buhari took office on May 29, promising to crush the group.
At the start of the year Boko Haram controlled territory about the size of Belgium.
The army said it pushed the group from most of that area in the last few months with the help of troops from Chad, Niger and Cameroon, but there has been a recent resurgence in militant attacks.