Meanwhile, former world champion sprinter Mathew Quinn says Van Niekerk has two key characteristics that have contributed to his success.
One is that he prefers to challenge himself rather than focus on rivals around him, and the other is that he thrives on the big stage.
Quinn , who had tipped Van Niekerk to break Johnson's 300m world best, says he "runs for himself, to challenge himself".
"He doesn't want to beat [400m rivals] Kirani James and [LaShawn] Merritt, etc, he wants to give his best. He just happens to smash everyone when testing himself," said Quinn, a 4x100m relay gold medallist at the 2001 world championships.
"In Jamaica he wanted the South Africa [200m] record and went out and got it," said Quinn, adding that Van Niekerk would lift his game even higher at the world championships in London in August.