Riots spread across Nigeria's north on Monday as results from presidential elections showed incumbent Goodluck Jonathan assured of victory in polls that reflected deep regional tensions.

Residents reported that a home belonging to an aide to the vice president was among those set alight and a mob sought to burn a Christian woman alive in one area.

Protesters fought running battles with soldiers in Nigeria's main northern city. A 24-hour curfew was imposed on the state of Kaduna, the governor announced on radio.

Rioting began in various states after allegations of vote rigging in Saturday's vote as results showed sharp divisions between the mainly Muslim north and predominately Christian south of Africa's most populous nation.

Observers have hailed the conduct of the poll, describing it as a major change from years of rigged ballots in the continent's largest oil producer.

But concerns have also been raised over extraordinarily high results for Jonathan in parts of his native south, including 99.63 percent in his home state of Bayelsa.

    In Kano, Nigeria's second-largest city, protests spread, with mobs armed with daggers, sticks and wooden planks taking up positions as police or soldiers sought to contain them. A shopping complex was set alight.