Witnesses say an explosion in the Nigerian city of Kaduna has killed at least seven people, including a three-year-old child.

Police say it was not immediately clear what caused Wednesday's explosion, though initial reports noted it happened near some cylinders of natural gas.

Several people were injured in the blast, and several shops were destroyed.

Kaduna sits in Nigeria's "middle belt" between the mainly Muslim north and mainly Christian south, and has been the scene of sporadic sectarian violence.

Rioting broke out in the city this April after President Goodluck Jonathan, a Christian, won the presidential election.

Nigeria's government has increased security across the north because of frequent bomb blasts and shooting incidents blamed on the radical Islamic sect Boko Haram.

Some information for this report was provided by AP and AFP.