BUENOS AIRES - South African Amber Schlebusch rallied late to secure gold in the girls' triathlon at the Buenos Aires 2018 Youth Olympics on Sunday.

The 17-year-old completed the course in 58 minutes and 45 seconds, 11 seconds ahead of second-placed Sif Bendix Madsen of Denmark. Switzerland's Anja Weber took bronze after crossing the line 51 seconds after Schlebusch.

China's Yu Xinying was 20th with an overall time of one hour, two minutes and 49 seconds.

"Now I can say I'm the Youth Olympic champion. It's a pretty good title to have so I'm really stoked," Schlebusch said. "I'm in this sort of disbelief right now."

Durban-born Schlebusch completed the opening swimming section in seventh place, some 27 seconds behind the leaders. The 17-year-old failed to make up ground in the bike section, slipping to eighth overall heading into the final running leg.

But she quickly hauled in her rivals, finishing the run more than a minute faster than Bendix Madsen.

"I knew that my weakest part was the swim," Schlebusch said. "And during the bike section I was in the pack at the back but nobody was really working so it was quite hard to close into the first two."

"I hadn't ever seen these athletes before so I didn't really know how they could do the run. I could see them in front though, even if they were quite far ahead. But on the run, that is where I put most of my confidence, and I just decided to catch them one by one. Take each one as it comes. I tried to close them down and it managed to work."

The Youth Olympics will run through to Oct 18.