The blasts occurred around 6:30pm (1730 GMT) in Molai, in the western suburbs of Maiduguri, where worshippers had gathered for evening prayers, the witnesses said and added that the bombers had slipped into the mosque disguised as worshippers.
“All the people in the mosque died. Not a single one escaped,” said Muhtari Ahmadu, a trader near the scene.
“We counted 42 dead bodies outside the mosque,” added Amadu Marte, a vigilante supporting the security forces in the fight against the Islamist Boko Haram group, which has carried out repeated attacks in the region.
Borno state police confirmed that the mosque was hit by twin bombings but gave a lower toll of about 14 dead.
Following the explosions, the mosque collapsed and injured “many people praying”, the police said in a statement.
“Casualties have been evacuated to UMTH (University of Maiduguri Teaching Hospital) and specialist hospitals in Maiduguri,” it added.
One of the attackers set off the first blast when he entered the mosque, they said. The second bomber detonated his explosives soon after, when many had rushed to the scene to help the first victims.
“When rescuers and sympathizers gathered in front of the place, the second one went off, killing many of them,” Marte said.
There was no immediate claim of responsibility for the attack but suspicion fell on Boko Haram, which was founded in Borno’s state capital Maiduguri in 2009.
The city has been hit repeatedly since President Muhammadu Buhari came to power on May 29 with a vow to crush the insurgency.