"Reduced rubber rounds" were used by public order police to disperse the stone-throwing crowd after their vehicles were also pelted with stones.
POPS members had to force open the gates in order to free the delegates that were trapped inside the hall.
By 9pm‚ some of the crowd moved to the N2 in Colchester where they attempted to close the road with burning tyres and objects and throwing stones at passing vehicles‚ the SAPS said.
A further nine vehicles including four trucks were damaged by these stone throwers.
The SAPS said their officials managed to clear the road and keep traffic flow open.
One 40-year-old man was arrested for taking a tyre to the N2. He will appear in court on Monday.
"Due to darkness and some of the street lights not working‚ more arrests were not possible as the stone throwers made use of the dense bushes next to the road."
Motherwell Cluster Commander‚ Major Dawie Rabie‚ appealed to the city "for the lights to be repaired and some of the dense bushes be trimmed".
"As SAPS we will not tolerate the damages caused to vehicles‚ buildings and infrastructure and the endangering of lives‚" he added.