Many people have been killed in three explosions during Friday prayers at one of the biggest mosques in the Nigerian city of Kano, reports say.

The Central Mosque is close to the Emir of Kano's palace and is where the influential Muslim leader usually leads prayers.

The Emir, Muhammad Sanusi, is currently in Saudi Arabia.

An eyewitness told the BBC he had counted about 50 bodies, but this figure has not been verified.

Other reports say some gunmen went on a shooting spree in the northern city after the blasts.

The militant Islamist Boko Haram group has targeted the city, the largest in northern Nigeria, several times during its five-year insurgency.

But most of its attacks are further east.

Earlier this month, the Emir called on people to defend themselves against Boko Haram.

At a prayer meeting he said residents should "acquire what they need" to protect themselves.

A police spokesman said the Emir's comments were a "call for anarchy" and should not be acted on.

The Emir, who until earlier this year was governor of Nigeria's central bank, normally stays silent on political matters.