A mosque in the Nigerian city of Zaria has collapsed during prayers, killing at least seven people, officials say.

Hundreds of worshippers were in the building at the time on Friday.

An investigation is underway to ascertain the cause of the collapse. The emir of the area told local media a crack had been discovered in one of the walls on Thursday.

The mosque is thought to be more than a century old. Nigeria has a long history of buildings collapsing.

"Four bodies were found initially," a council spokesman Abdullahi Kwarbai told Reuters news agency.

"Then three others were found after the rescue team searched the collapsed mosque," Mr Kwarbai added.

A team of engineers had been organised to fix the crack in the building, the Emir, Mallam Ahmed Nuhu Bamalli, told Punch News.