Police officers who had arrived to disperse stone-pelting youth at Kamukunji Grounds were forced to retreat.
For a moment, officers had managed to send away all the youth but they were overpowered and retreated towards Jogoo Road.
Water cannons were seen arriving at the grounds to support retreating officers.
Several roads in the area have been barricaded by the protesting youth.
Earlier, violence almost erupted at the venue when police officers attempted to stop the youth from convening at the grounds.
Some youths threw stones at the officers, who immediately left the area.
A dias was being erected at the venue and a public address system was to be mounted in preparation for the rally.
