Olympic 200m backstroke champion Kaylee McKeown cruised to the Australian title Saturday as fast-rising prospect Mollie O'Callaghan punched her ticket for a fourth individual event at next month's world championships.

The 20-year-old McKeown, who won the 100m and 200m backstroke at last year's Tokyo Olympics, touched in 2mins 05.31secs in Adelaide -- the fourth quickest of the year and with plenty in the tank.

But it was a long way outside the 2:03.35 world best set by American arch-rival Regan Smith in 2019.

"This is a little bit of extra training under my belt and hopefully in a few weeks with a little more rest I can produce a faster time," McKeown said poolside as she warms up for a showdown with Smith in Budapest next month. 

"Over and done with now and I'm happy."  

McKeown holds the 100m world record and Olympic title and won that race on Friday in 58.49.

She also swam a blistering 400m medley, but is expected to drop it from her programme for the worlds.

Veteran Emily Seebohm, the Tokyo Olympic 200m backstroke bronze medallist, is taking a break and not contesting the Australian titles, with O'Callaghan, 18, qualifying alongside McKeown.

O'Callaghan has been a standout in Adelaide, winning the 100m freestyle in 52.49 to claim the number one world ranking this year, while her 200m freestyle was good enough for second behind Olympic gold medallist Ariarne Titmus. 

She also won the 50m backstroke and has now finished second to McKeown over the 100m and 200m backstroke.

The 50 stroke races at the trials do not decide who qualifies for the worlds and Commonwealth Games in July, with selection at the discretion of Swimming Australia.

"It was so good to get a PB (personal best) and so glad it's done now," said O'Callaghan, who won two relay golds in Tokyo, after posting 2:08.48. 

"It's been amazing and crazy that I have an individual spot (at the worlds), and so many now."

Tokyo Olympic bronze medallist Brendon Smith won the men's 400m medley by nearly three seconds in 4:11.88 to bag the double after also clinching the 200. Lee See-Bom came second in both races and will also be on the plane to Hungary.

"Was hard backing up from the 200 but pretty happy with that result," said a relieved Smith.

Olympic 100m freestyle silver medallist Kyle Chalmers was not contesting the event in Adelaide, instead focusing on butterfly, in which he qualified for the worlds in the 50m and 100m.

In his absence, William Yang (48.55) touched by a fingertip ahead of Zac Incerti (48.65), with both making the Budapest cut.

Lani Pallister hit the wall first in the 1500m in a personal best 15:55.40, an event her mother Janelle won three times.

It was the fourth quickest time of the year behind Americans Katie Ledecky and Katie Grimes. Pallister also won the 800m.

Meanwhile, Holly Barratt became the oldest woman to win an Australian national title aged 34, winning the 50m fly in 26.02.