Militants believed to be from Boko Haram have stormed a bus in Cameroon, taking 20 people hostage and killing 12 of them.

Suspected members of Boko Haram have kidnapped 20 people from a bus in northern Cameroon, then executed 12 of them, a security source and resident says.

The kidnapping occurred on Sunday and all of the survivors have since been released, said a resident, on condition of anonymity, whose wife was among those abducted.

An official from a local NGO also confirmed the incident. According to the security source, who is based in the region, the victims were travelling in a bus stormed by alleged Boko Haram members.

"The bus was coming from Koza and was travelling to Mora," the source said, referring to two towns in the country's extreme north near the Nigerian border.