An armed gang in Nigeria has killed a local policeman and abducted a German construction worker in an ambush in Kano, the biggest city in the north, police say.

The gang of five opened fire on their vehicle as they were travelling to a construction site, police added.

A "powerful" team of officers has been deployed to hunt down the gang, and rescue the German national, police said.

The motive for the abduction is unclear.

In some cases, criminals kidnap people for ransom while in other cases militant Islamists take them hostage.