At least 63 people died during the removal of a sack of home-made bombs found at an abandoned camp of terror group Boko Haram.
The incident occurred in the restive Borno state where civilian self-defence fighters were patrolling the area when they came across the bag and carried the bombs to the nearby town of Monguno, witnesses told AP.
Who are Nigeria's Boko Haram terrorists?
Boko Haram (recently renamed Iswap) fights against Western influence in Nigeria and aims to impose its version of Sharia law on the country. The group declared an Islamic caliphate in Gwoza, along the Cameroon border, in August 2014.
Boko Haram has raided several cities in the north of the country in a bid to take control of more land.
Three states − Adamawa, Borno and Yobe − have been under a state of emergency since May 2013, due to Boko Haram's attacks.
The group has killed at least 2,600 people since the beginning of 2015. More than 200 have been killed since the beginning of June.
"It's very sad because most of those killed and injured are young men, with a small number of females," Haruna Bukar said, adding that people wounded in the incident are being treated at the hospital.
Boko Haram uses bombs and other explosive devices during suicide missions and raids in villages across the north east of the country, where AP estimates that at least 200 people have been killed in suicide attacks since April.
Unicef warned that Boko Haram's use of women and children in suicide missions is increasing in Maiduguri, capital of Borno, and estimated that more suicide bomb attacks have occurred in the north east since the beginning of 2015 than in the whole of last year.
Abbas Gava, a spokesman for the civilian fighters, said: "This also further heightens our fears of the need for a lot of sweeping to be done by the explosives ordnance department before people are allowed to go back to their liberated homes."
The incident occurred one day after eight policemen were killed in a bomb attack in Damboa, Borno.
Boko Haram is also suspected of being behind a terror attack that occurred outside the police headquarters and academy in Chad's capital N'Djamena that killed dozens of people in June.
The Nigerian government is being aided by mercenaries and troops from Chad, Benin, Niger and Cameroon in its offensive and has scored some successes since the military co-operation started in February.
Newly elected president Muhammadu Buhari, a former military chief, vowed Nigeria would do anything it can to defeat the deadly insurgence and find some 220 girls who were kidnapped by Boko Haram in Chibok, Borno state, in April 2014.