Nelspruit - A group of protesters set alight a bus when they barricaded the N4 near Witbank on Wednesday, Mpumalanga police said.
They barricaded the Vosman and Wakefield street intersection around 6am, Brigadier Selvy Mohlala said.
Two cars were damaged when the group threw stones at passing vehicles.
Police dispersed the group and the road was cleared. No injuries were reported and no arrests made.
Mohlala was unable to provide a reason for the protest.