The Proteas, who chose to bat under cloudy skies, found themselves struggling at 24/4 with the dismissals of key batsmen, including skipper Temba Bavuma and Quinton de Kock.
Scorecard: South Africa vs Australia
However, rain intervened, bringing the Proteas respite with the score at 44/4. Heinrich Klaasen and David Miller were at the crease when the players were forced off the field at Eden Gardens.
Breaking: India enter World Cup 2023 final, beat New Zealand by 70 runs
If the semi-final action falls victim to the weather conditions on Thursday, a reserve day on Friday is in place to accommodate any disruptions.
And if no result is possible on the reserve day too, then South Africa would be declared the winners based on their higher position than Australia in the league phase standings.
The winner of this semi-final will face undefeated hosts India in the World Cup final at Ahmedabad on Sunday.