Ariarne Titmus has smashed the 200m freestyle world record in a thrilling race against former record holder Mollie O'Callaghan at the Australian Olympic trials in Brisbane.

Titmus clocked 1:52.23, smashing compatriot O'Callaghan's previous mark of 1:52.85, with her St Peter's Western teammate stopping the clock in 1:52.48.

"The world record is a bonus," Titmus said.

"Honestly, since Tokyo I've reflected a 1:52 swimmer every day in training, so I'm happy to finally put it together and put together a swim that I know I'm capable of.

"It's exciting to do it in my hometown in front of the hometown crowd, but it gives me really good confidence for the Olympics."

Titmus said she had not been using O'Callaghan holding the record as motivation.

"I don't look at who has it," she said.

"I look at the time and honestly, that wasn't really on my radar coming into this. I just really wanted to put together a great swim."

"Yes girls, yes girls," growled coach Dean Boxall in the mix zone as his two charges addressed the media, echoing the sentiments of everyone at the Brisbane Aquatic Centre.

The crowd — the biggest of the week so far — did not need much of a push to be on their edge of their seats ahead of a race as anticipated as any on the programme.

There was enough excitement being generated in the build-up to fuel the energy required to blare the base-heavy music out of the speakers, throw up the flames from the top of the entry wall and spin the lights that swung wildly around the 1982 Commonwealth Games pool.

The tension was palpable.

In the pre-session warm up, coaches stared intently at stopwatches as if trying to discern the magic formula for success.

Swimmers peered up from the pool, desperate for their sages to share whatever it is those numbers told them.

Numbers can only tell you so much, but the numbers ahead of this 200m free told us plenty.

In the past 12 months, O'Callaghan has swum four of the seven fastest times in the world, with Titmus swimming the second fastest time in that period too.

Six of the eight fastest times ever belong to Australians.

Five Australian swimmers sit among the world's top 18 fastest swimmers for the distance over the past year — and four of them were in the final.

World record holder O'Callaghan. 

Reigning Olympic champion Titmus.

Then a cast of blockbuster proportions behind them: Fellow world record holders in the 4x200m freestyle relay Brianna Throssell and Shayna Jack, plus heat swimmer for that World Championship winning team Lani Pallister.

This was, as Jack said in the morning, "stacked".

Such is the power of Australian women's swimming. 

Such is the allure of a spot in a relay team desperate to right the wrongs from a bronze-medal finish in Tokyo three years ago.

This was a race not to be missed and it didn't disappoint.

As the combatants were introduced all eyes went to the centre of the pool and that's where the thrilling race unfolded.

Jack took the race out down the first 50, but after that it was all Titmus and O'Callaghan, the 400m champion leading the 200m star stroke-for-stroke. 

As O'Callaghan charged down the final length, Titmus held her nerve and stroke together to dip under the 1:53.00 mark for the first time.

"I'm just in pretty good form," Titmus said.

"My 400 was great, I think I took confidence from that. I've taken confidence from my training the past six weeks. 

"I've done some things in the pool that I haven't done before and so you have to use that."

Titmus and O'Callaghan led home Lani Pallister of Griffith University in third spot, followed by three more of Boxall's swimmers, Brianna Throssell in fourth and Shayna Jack and 19-year-old Jamie Perkins, who dead-heated for fifth.

All six went under the qualification time.