World record holder Ariarne Titmus fired a warning shot on Friday to Katie Ledecky and Summer McIntosh ahead of the Paris Olympics with the fastest 400m freestyle of the year.

The reigning Olympic champion went under four minutes at the Australian championships on the Gold Coast, hitting the wall in 3min 59.13sec to remain unbeaten in the event since 2019.

Titmus beat Ledecky in a thrilling final at the Tokyo Olympics then broke the American great's long-standing world record in 2022, only for Canadian teenager McIntosh to better the mark last year.

The Australian hit back to reclaim the world record months later with the expected clash between the three in Paris shaping as a blockbuster.

"That's a good sign," said Titmus, who is again set to contest the 200-400-800 treble in France. She won gold over 200 and 400 in Tokyo and silver behind Ledecky in the 800.

"I'm just trying to think about my expectations on myself and what I expect to do in Paris."

"I know a lot of people are willing me on and I'm just trying to use it in the best way possible," added the 23-year-old, who has swum four of the six fastest times in history.

Lani Pallister finished second in a personal best 4:01.75 ahead of the Australian Olympic trials in June.

After her Australian record-breaking exploits in the 200m and 400m medley, Kaylee McKeown was again on fire in the 50m backstroke -- a non-Olympic event in which she holds the world record.

The 22-year-old powered to a 27.07 finish ahead of Mollie O'Callaghan (27.16) in the fifth fastest time ever.

"Had a bit of fun trying to change gears this meet, it's been good training," said McKeown, who is also the 100m and 200m backstroke world record holder.

Matt Temple signalled his Paris intentions with the quickest 100m butterfly of the year, surging to the wall in 50.80.

Former world champion Cameron McEvoy and sprint king Kyle Chalmers both went under 22 seconds in the 50m freestyle, with the former taking the title in 21.93 as he looks to make a fourth Olympics.

Elijah Winnington continued his stellar form with victory in the men's 800m freestyle, powering home in 7:43.08 by half a length from Sam Short.

Winnington set a world-leading time this year in the 400m free earlier in the meet.

In other races, William Petric touched first in the 200m medley in 1:58.43 ahead of New Zealand's Lewis Clareburt, the 400m medley world champion.