DA leader Mmusi Maimane taking a selfie with supporters on Wednesday.
The DA said on Wednesday that it was "very pleased with the high number of South Africans who have come out to vote".
"We are closely monitoring the voting process, in an effort to protect the integrity of the election," DA spokesperson Solly Malatsi said in a statement.
He said the party logged a number of issues with the Electoral Commission of South Africa (IEC).
"We call on the IEC to look into and resolve these incidents as a matter of urgency."
The DA said it was "encouraged to see thousands of South Africans, who have been brave and have chosen to give change a chance, in many parts of the country braving the cold and the rain in so doing".
"The people of South Africa are desperate for change and they know that the DA is the only party that can bring true, tangible change that will turn things around for all South Africans," Malatsi said.
The party said its leader, Mmusi Maimane, and all nine DA premier candidates had already cast their votes.
It urged all South Africans to follow suit and come out in their numbers to vote for a better future.
"We implore on South Africans who have not yet voted, to take their smart cards or the green bar-coded South African IDs to their nearest voting stations to cast their votes."
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