Johannesburg - An Electoral Commission of SA (IEC) centre was set alight by residents of Alexandra, Gauteng police said on Friday.
A room in a community centre which was used by the IEC was burned by residents on Thursday night, Brigadier Neville Malila said.
There were people inside the centre at the time of the fire, but no injuries were reported.
Thirty-one people were arrested and are expected to appear in court soon.
Malila said the motive was unknown. - Sapa