Kano - A blast ripped through a bus station in Kano as passengers boarded buses out of the city, witnesses said.
Explosives, apparently concealed in a bag that was abandoned by two men disguised as travellers, went off at about 3:00 pm (1500 GMT) at the New Motor Park in the predominantly Christian Sabon Gari neighbourhood of the city.
There was no immediate indication of the number of casualties, people at the bus station told AFP.
Kano, Nigeria's second city has been hit before by explosions, with blame attributed to Boko Haram militants, who have been waging a violent insurgency in the country's north since 2009.
On June 23 a bomb blast at a public health college in the city killed at least eight while on May 19, a suicide car bomb attack in Sabon Gari killed at least four people, including a young girl.
At least four strong explosions rocked the same area on July 29 last year, killing 12.
In the latest blast, market trader Suleiman Bala, who was at the bus station, said: "Two men came into the motor park with a black bag disguised as travellers taking a bus out of the city.
"They left the bag among rows of buses and slipped away and the explosive went off soon after. Many people were affected but I can't give a number because everyone ran out in confusion."
The two suspects were noticed when they came in but could not seen after the blast, said another witness, Matthew Ebere.
"They came in with a bag and everyone thought they were travellers taking a bus and the explosion came from the area they stood for a while."
Abdullahi Habibu, a mechanic in a nearby garage, said he saw a young man drenched in blood running out of the garage shouting for help.
"He was covered in blood which kept gushing from his head and kept shouting for help as he ran towards El-Dorado cinema," he added.