Defending 50m backstroke world champion Kaylee McKeown appeared to have her hopes of defending the crown dashed, after being disqualified from her heat on the opening day of the Australian Swimming Trials.

McKeown, who is the reigning world champion in the women’s 50m, 100m and 200m backstroke, qualified fastest for Monday night’s final in the 50m backstroke. 

But the current world record holder was disqualified after officials ruled she had taken off too early in her heat.

However, McKeown will line up in Monday’s final after successfully arguing she had been distracted by movement just before the starting siren. 

McKeown qualified with a time of 27.27 seconds, just ahead of Mollie O’Callaghan, who was second fastest with 27.72.

Both were under the qualifying times for next month’s World Aquatics Championships in Singapore. 

Meanwhile, Lani Pallister was the fastest qualifier for the women’s 400m freestyle. 

The women’s 400m freestyle has been a hot topic in swimming circles after Canadian star Summer McIntosh demolished the world record over the weekend. 

McIntosh bettered the previous mark, held by Australian Olympic champion Ariarne Titmus, by a massive 1.2 seconds. 

“It’s so insane to be racing at a time when there’s been three generational talents,” Pallister said of McIntosh’s benchmark. 

“If you look at the big three for women’s distance swimming … Arnie (Titmus), Katie (Ledecky) and Summer (McIntosh). It’s really incredible.”

TItmus will not be participating at this week’s swimming trials after electing to take a year away from competitive swimming.