Shopkeepers and vendors have been resisting an anti-encroachment campaign launched by traffic police a few days ago.
They took out a procession on Sunday and pelted policemen with stones, tomatoes and potatoes.
They set on fire a motorcycle of traffic police and burned tyres on the Alamdar road, Mission road, Toghi road and Meezan chowk.
Some shots fired at police caused a clash in which four protesters and a policeman were injured. Some shopkeepers accused traffic police personnel of firing on protesters. Police, however, rejected the allegations.