The blasts in Jos happened at a makeshift market near the Terminus bus station, which had been set up after a twin car bomb attack in May that left at least 118 people dead.
Mohammed Abdulsalam, coordinator for the National Emergency Management Agency (NEMA) in the city, said the scene of the attack was a densely populated area.
"The bodies recovered so far are 31 but rescue workers are at the scene and the figures may change," added Pam Ayuba, spokesman for the Plateau state governor Jonah Jang.
It has been targeted by Boko Haram Islamists in the past but is also a hotbed of ethnic and sectarian tensions that frequently boil over into deadly violence.
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In Kano, a senior security source and a nurse said a 13-year-old was arrested on Wednesday after she and a male accomplice walked into a clinic seeking medical treatment.
The location of the clinic -- some 20 kilometres from the scene of a double suicide attack by two women on a textile market just hours earlier -- raised suspicions.
"On searching her, the police discovered explosives hidden under her hijab, confirming our suspicion. They took her and the man accompanying her away."
The senior security source said the young girl was from the northeastern state of Bauchi and had been part of the "suicide team" that attacked the busy Kantin Kwari textile bazaar.
Four people were killed in that attack and seven others injured.
"Her arrest is a huge breakthrough in unravelling the spate of suicide attacks by young girls in the city," the source added.
Just last month, at least 120 people were killed when two suicide bombers blew themselves up at Kano's central mosque and gunmen opened fire on worshippers as they fled.