Security forces are pictured as smoke is seen in the background during a protest in Abuja, Nigeria. (File photo)

Dozens of people burnt to death on a bus in Nigeria after gunmen attacked them and torched their vehicle in a northwestern state, police say.

Gunmen, known locally as bandits, attacked the bus in Nigeria’s Sokoto State on Tuesday, police and residents said.

The bus was carrying 24 passengers when it was set alight by the armed men. Seven people escaped with injuries and were taken to hospital, according to Sanusi Abubakar, spokesman for the northwestern Borno State police.

Citing residents, Reuters reported that the bus was overloaded and the bodies were burnt beyond recognition. It said at least 30 bodies, including those of women and children, were counted.

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

Northwestern Nigeria has long been wracked by violence involving clashes over land between rival communities, attacks by heavily-armed criminal gangs, and reprisal killings by vigilante groups.

Gangs of thieves and kidnappers have been terrorizing communities in the region, where they raid schools, masques, and markets, killing and burning buildings after looting them.

The gangs have been infiltrated by Boko Haram and other terrorist groups.

Nigerian President Muhammadu Buhari has come under fire for the worsening security situation in several regions of the country.