Gunmen kidnapped dozens of worshippers attending Friday afternoon prayers at a mosque in Nigeria's Northwestern state of Zamfara, police and witnesses said.

Armed gangs are rife across Nigeria's Northwest where they rob or kidnap for ransom, and violence has been increasing, where thinly stretched security forces often fail to stop the attacks.

Mohammed Shehu, Zamfara police spokesman said an unknown number of worshippers had been abducted from Jumu'at central mosque in Zugu town, Bukkuyum local government area.

Zugu is 170 km (106 miles) west of Zamfara state capital Gusau.

"The Zamfara state police command in collaboration with military and vigilantes have dispatched personnel for the search and rescue operation," he said.

Ibrahim Aminu, who was at the mosque told Reuters that the gunmen hid guns under their garments and pretended to be worshippers.

On entering the mosque compound, they pulled out their weapons and fired in the air, forcing people to run for cover, he said. The gunmen took dozens of worshippers and force-marched them to an unknown place.

Mohammed Bukar Zugu said his 22-year-old brother was among those kidnapped. The gunmen later used his phone to call him and asked that he prepare a ransom. They did not say how much they wanted, he said.

Nigeria's military last month started launching air strikes against the armed gangs, known locally as bandits and says it has so far killed dozens of them.

Reuters