Many media outlets in South Africa support the African National Congress, professor Anton Harber said on Thursday.

"In South Africa, we have a growing, increasingly dominant network of ANC-supporting media, supported by the state through the front or back door," the University of Witwatersrand journalism professor said at media diversity round table discussion in Johannesburg.

"This is a historical correction and certainly it is an advance on the situation where only one newspaper in 1994 unequivocally called on voters to vote ANC."

Harber said the practice should however be stopped if the independence and accountability of journalism continued to shrink.

"I'm not concerned about whether a publication supports or opposes the ANC. I am more concerned whether the culture of that newsroom is an open one that encourages a diversity of views and opinions," he said.

"And this is important for one simple reason - journalism is at its best when it is critical, probing, disruptive and discomfiting. Journalists are at their best when they make trouble for those with power and authority."