At least 51 people have been killed after twin car bomb blasts went off at a bustling marketplace in Nigeria's northeastern city of Maiduguri, a Red Cross official said.
The first blast came from a passenger car and did not cause many casualties, said Hassan Ali, the leader of an anti-terror vigilante group.
Most of those killed in Saturday's attacks had run to the scene to help when a second explosion blasted from a pickup truck carrying firewood, he said.
The attack in the birthplace of the armed group Boko Haram is the latest in a string of deadly assaults to hit the West African country.
Boko Haram, blamed for widespread violence in the north east, did not claim responsibility for the blasts.
The AP reported that many more people were believed buried in rubble from the night explosions that collapsed some buildings.
Other buildings caught fire with smoke billowing for hours, the AP added, citing the Red Cross official.
The victims included children who were dancing at a wedding celebration and people watching a soccer match on an outdoor TV screen, survivors told the AP.
Survivors said they captured a man who jumped out of the first car, grabbed a tricycle taxi and tried to make off.
He was badly beaten and taken to nearby Umaru Shehu General Hospital, where a security guard said all the wounded brought in had died.
Most spoke on condition of anonymity for fear of reprisals.
It was not known how many wounded are being treated in at least three hospitals in the city.
The attack is a major setback to a new army and air force offensive against the Boko Haram uprising under new commanders since President Goodluck Jonathan fired his entire military command.
Since then, criticism and anger have grown as attacks by the armed group have increased and become ever deadlier. More than 300 people were killed in February alone.
The Defence Ministry has blamed recent attacks on fighters escaping from daily aerial bombardments and ground assaults aimed at flushing them out of forest hideouts and mountain caves along the border with Cameroon.
The military closed hundreds of kilometers (miles) of border with Cameroon last week, saying it wanted to stop extremists escaping across the border and using the neighbouring country to launch attacks.