“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.
The bombers slipped into the mosque disguised as worshippers, witnesses said.
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.
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.
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.
Boko Haram claimed responsibility for three suicide attacks in the satellite towns of Kuje and Nyanya outside Nigeria’s capital Abuja on October 2, which killed a total of 18 people and injured 41.
Nigeria’s military claims the Islamist militants are a spent force and that troops have driven them from their camps and occupied territory in the remote region.
But guerrilla-style attacks have continued, including across the border. At the weekend, 41 people were killed in triple explosions in Baga Sola, on the Chadian side of Lake Chad, where Nigeria meets Niger, Chad and Cameroon.
The four countries have launched a joint offensive against the Islamists.
Their mission received a boost on Wednesday when US President Barack Obama said he was deploying up to 300 military personnel to Cameroon for intelligence, surveillance and reconnaissance operations against Boko Haram insurgents.
At least 17,000 people have been killed and more than 2.5 million made homeless since Boko Haram began its bloody campaign