Kidnappers have released 53 people including women and children they seized on a bus in Nigeria, local authorities said, while dozens of others taken from a school in a separate incident are still missing.

Criminal gangs known locally as "bandits" in northwest and central Nigeria have scaled up attacks in recent years, kidnapping, raping and pillaging. 

A gang last week had seized 53 people, including 20 women and nine children, who were travelling on a state-owned bus in Kundu village in Niger State.