EFF leader Julius Malema says the party is investigating a video in which people who appear to be EFF supporters drag an elderly woman - who is wearing ANC colours - off a chair before beating her.
"I saw the video, and we are investigating," Malema tweeted as ballot counting continued.
The party's spokesperson was not immediately available to elaborate.
The ANC said it was also looking into the matter.
The video was posted on Twitter by "La Kosi" and a message asking for more information and for details on the woman's condition has been sent to her.
Some have suggested it occurred at a North West voting station, but this has not been confirmed.
Betty Diale, EFF chairperson in the province, said she had seen the video but did not know any further details.
La Kosi tweeted: "Are these the people who claim to respect the elderly? Are these the very same people that promise our elderly grants worth more than what they are receiving whilst they lack empathy? Hayini bethunana!"
The responses mostly expressed dismay and a few suggested it was about alleged double voting. Some claimed the woman deserved it.
"She's a criminal, she must be treated as such. They must still jail her for 10 years. Trying to vote twice. Still there's no beating here" tweeted @K_Kulture00
Mothusi Shupinyane, spokesperson for the ANC in the North West said: "We have not heard the claims yet but we would like to investigate it quickly before we can respond. I must also confirm that we had seen the video making rounds yesterday on social media."
The IEC's provincial electoral officer, Dr Tumelontle Thiba, said they had not received a complaint regarding the incident, but they were looking into it.
Comment was not immediately available from the national IEC, but it is understood that it is aware of the video.