But players past and present, including India captain Virat Kohli, have been critical of the move.
South Africa have come out in support of four-day Test matches, refuting reports that said they would oppose the plan.
The International Cricket Council is set to discuss the idea of making Tests four-day games to ease a crammed international calendar and reduce player workload.
England have said they will support the idea after 2023 while Australia are to give serious consideration to the plan.
Britain's Daily Mail newspaper reported that South Africa would oppose the idea, despite the country becoming the first to host a four-day Test when they played Zimbabwe in 2017.
"In view of an unsourced and misleading report in the media this morning, please be advised that it is Cricket South Africa’s official policy to support four-day Test match cricket," Cricket South Africa said in a statement.
"We, in fact, hosted the first official four-day Test match between ourselves and Zimbabwe a couple of years ago."
South Africa beat Zimbabwe by an innings midway through day two of that Test in Port Elizabeth.
The powerful Board of Control for Cricket in India (BCCI) has yet to offer an opinion, but India captain Virat Kohli said he was totally against the plan.
"I am not a fan," Kohli told reporters.
"I think the intent will not be right then because then you will speak of three-day Tests, I mean where do you end?
"Then you will speak of Test cricket disappearing. I don't endorse that at all."