At least 30 passengers on a bus in Sokoto state were burnt to death when gunmen torched it on Tuesday, police and residents said, in yet another reminder of growing insecurity in Africa's most populous country.

Gunmen, known locally as bandits, have in the past year carried out violent attacks targeting villagers and commuters travelling on highways and kidnapped hundreds of school children for ransom in the north of the country.

Sanusi Abubakar, spokesman for Sokoto state police, said the bus was carrying 24 passengers when it was set alight by armed men and that seven people had escaped with injuries and taken to hospital.

But two residents who reached the scene and helped retrieve bodies told Reuters that the bus was overloaded and the bodies were burnt beyond recognition.

They counted body parts of at least 30 people, including women and children.

The residents said the villagers were ambushed on a road linking the Sabon Birni local government area and the village of Gidan Bawa in Borno state.

Bandits move around on motor-bikes and are known to hide in forests, where they often keep kidnapped victims while awaiting ransom payment.

Reuters