More than 70 people have been killed in two blasts that rocked a crowded bus station on the outskirts of Nigeria's capital, Abuja, officials say.
The blast happened as commuters were about to board buses and taxis to go to work in central Abuja, the BBC's Haruna Tangaza reports.
Eyewitnesses say there are dead bodies scattered around the area.
Suspicion immediately fell on the Boko Haram Islamist militant group, which has staged previous attacks in Abuja.
However, most of its attacks have been in the north-east of the country.
Abbas Idris, head of the Abuja Emergency Relief Agency, told the BBC that so far they have confirmed 71 people dead and 124 injured.
Eyewitness Badamasi Nyanya said he had seen 40 bodies being evacuated; other eyewitnesses say they saw rescue workers and police gathering body parts.
The blast ripped a hole four feet deep (1.2 metre) in the ground of Nyanya Motor Park, some 16km (10 miles) from the city centre, and destroyed more than 30 vehicles, causing secondary explosions as their fuel tanks ignited and burned, the Associated Press news agency reports.
Ambulances have been taking the dead and injured to nearby hospitals.
Eyewitness Mimi Daniels, who works in Abuja, said: "I was waiting to get on a bus when I heard a deafening explosion then smoke," she told Reuters.
"People were running around in panic."
Another eyewitness told the BBC: "I have never seen [anything] like that in my life. It was just terrible... We were just running helter-skelter. So somehow I think that they planted something inside one of the buses there.
"So there are many dead shot down at the scene of the accident. And as you can see now some of these casualties... we are hoping, we are praying they will be ok. We saw some ambulances bringing corpses to other hospitals."
He added it was difficult to estimate how many had been killed in the attack, but that there were many.
This year, Boko Haram's fighters have killed more than 1,500 civilians in three states in north-east Nigeria, says the BBC's Will Ross in Lagos.
Boko Haram has hit Abuja several times before, including an attack on the United Nations building in 2011.
The Nigerian government had said the violence was now contained in a small area of the north-east.