BRISBANE, Australia (AFP) — Olympic 100-meter freestyle champion Emma McKeon will not defend her title in Paris after missing out on qualifying Friday with Mollie O'Callaghan and Shayna Jack securing the two Australian slots at stake.

O'Callaghan surged home on day five of the Australian trials in Brisbane in 52.33 seconds with Jack (52.72 seconds) second ahead of a top-class field.

No other country, including the United States, can boast such depth over the distance, with seven of the eight finalists under the qualifying time.

Meg Harris and Bronte Campbell came third and fourth to be part of their formidable 4x100-meter relay team, who are not only Olympic champions but hold the world record and the eight fastest times in history.

McKeon, Australia's most decorated Olympian with 11 medals, including five gold, could only manage sixth behind teenager Olivia Wunsch.

The 30-year-old McKeon had already booked a ticket to France in the 100-meter butterfly and will still be part of the relay squad with six swimmers traditionally allowed.

"It's a very tough race to be in. The 100 free has so much depth in it, and all these girls I respect so much and they're so inspirational," said 2023 world champion O'Callaghan, whose 200-meter freestyle world record was shattered by Ariarne Titmus this week.

"A little bit disappointed at the time, but that's something I can work on for Paris."

Jack, who missed the Tokyo Olympics while serving a ban over an anti-doping rule violation she always denied, was emotional afterwards.

"I honestly have no words. It probably was a swim I thought I wasn't capable of," she said, fighting back tears.

Such is Australia's talent that Tokyo bronze medallist Cate Campbell, striving to make a fifth Olympics, didn't even make the final. Neither did Titmus or Kaylee McKeown, who both contested the heats.

But in a sign that Australia's factory-line of top sprinters shows no sign of slowing, 18-year-old Wunsch and 17-year-old Milla Jansen both did so.

Zac Stubblety-Cook ensured he will be in Paris to defend his 200-meter breaststroke crown.

The 25-year-old, who lost his world record last year to China's Qin Haiyang, hit the wall first in two minutes and 07.40 seconds ahead of the rapidly improving Joshua Yong (2:08.08) who also qualified.

"It's awesome. It's always about bringing it home with everything you've got and leaving nothing in the tank," said Stubblety-Cook, who owns three of the top five times ever.

It made amends for unexpectedly missing out in the 100m breaststroke, an event that saw Yong qualify.

Teenager Ella Ramsay produced a storming final 50m to win the women's 200 breaststroke ahead of Jenna Strauch in 2:22.87 to also make the grade.

In the men's 200m backstroke, Bradley Woodward (1:56.22) and Se-Bom Lee (1:57.02) both cleared the Olympic cut to book their places.

Sam Short, a potential medal contender in the men's 1500m freestyle, pulled out with illness, but could still swim the race in Paris as he was already on the team after qualifying for the 400 meters.