Multiple explosions have ripped through Nigeria's northern city of Kano, one blast believed to have been targeting police headquarters Friday, causing unknown casualties, although details were not readily available.

The blast occurred just after 5 p.m. in Kano, the largest city in Nigeria's Muslim north and the second largest in the country. Reporters were kept away from the building, which had its roof blown off in the explosion, according to The Associated Press.

An AP reporter also said a plume of smoke could be seen rising from another neighborhood in the city. And another witness said the explosion was powerful enough to shake his car several times.

The explosions caused pandemonium in the city as motorcycles and cars fled the areas.

Scores of bomb blasts have rocked Nigeria's north as Boko Haram, a radical Islamist sect has increased its bloody campaign of violence.

The Islamist group, which aims to impose Sharia Law across the country, was responsible for a series of bombings that killed more than 40 Nigerians on Dec. 25; it also claims responsibility for a series of Christmas bombings in 2011, as well as an attack last year on United Nations headquarters in Abuja.

Nigeria is a country divided between the mainly Muslim north and the largely Christian south.

The sect killed at least 510 people last year.