The Independent Electoral Commission (IEC) said it would conduct an audit of results and votes cast in a sample of voting stations to ascertain if double voting had occurred in the national elections, chief electoral officer Sy Mamabolo said on Thursday.

This comes after the IEC in KwaZulu-Natal said 20 people were arrested in the early hours of the morning in relation to "fraudulent incidents" and political parties raised concerns about voters' ability to hop from voting station to voting station on election day, and potentially cast their vote several times.

Several voters had showed that the ink used to stain their fingers had disappeared, just hours after casting their ballots.

Indelible ink was one of the security measures used to protect the voting system and prevent people from voting more than once.

The IEC said it has ordered an investigation into the effectiveness of the indelible ink marker pens supplied for the elections. 

Mamabolo said the audit would cover a representative sample of voting stations as well as all voting stations where complaints or allegations of double voting have been received. 

"The audit will involve the capture of information showing the ID numbers of voters who cast votes at each voting station from the 'zip-zip' scanners and completed VEC 4 forms," he told reporters at a media briefing in Pretoria.