Kyle Chalmers books spot at Olympics 2024 in Paris but former love rival Cody Simpson has just ONE final shot at making it to Games with girlfriend Emma McKeon

Kyle Chalmers reigned supreme in the pool as he booked his place at the Paris Olympics with a blistering effort in the men's 100m freestyle.

Aussie champion Chalmers, who won gold in Rio and silver in Tokyo in the event, stormed a packed field of talent to win his trial for the Paris Games next month.

But it was not meant to be for celebrity swimmer Cody Simpson, who failed to make it out of his heat in his first bid to become an Olympian.  

Simpson ranked 10th in the heats with a time of 49.04 seconds. The eighth quickest, Max Giuliani, secured a spot in the final by clocking 48.90.

The 27-year-old, who hit pause on his pop career to return to swimming, has one more chance to make Australia's swim team for next month's Paris Olympics.

Simpson , who is dating Aussie Olympic legend and Chalmer's former girlfriend Emma McKeon, will race his preferred 100m butterfly on Saturday.

'It's a stacked field in the 100 free so I knew it was going to be a bit iffy trying to get in to that final,' Simpson said.

'It's a good warm-up for the 100 fly.

'I have had a really good last six months of training just absolutely flogging myself.

'Swimming is tricky ... you're training for a long time for really marginal gains, microscopic sometimes.

'I have just been banging at the brick wall trying to get to that next level. And the faster you get, the harder it is to keep getting faster.'

Chalmers touched in 48.39 ahead of William Yang (48.50) and Flynn Southam (48.64).

'I probably didn't execute to the best of my ability ... definitely some areas I can improve on tonight,' Chalmers said, looking forward to the final.

'I will really put the pressure on myself ... it has got to be self-driven and self-motivated.'

Also on Thursday morning, Kaylee McKeown topped the times in the 200m backstroke heats.

The reigning Olympic champion and world-record holder in the event finished in two minutes 08.83 seconds with Hannah Fredericks (2:10.19) the next quickest.

Emily Seebohm, aged 32 and just eight months after giving birth, also advanced to the final.

Seebhom, bidding to become the first Australian swimmer selected for five Olympics, clocked 2:11.00 to be fourth-fastest qualifier.

'When I was pregnant, I felt like I lost that athlete that I was,' Seebohm said.

'And this is me trying to regain what I once had and proving to other women that it's possible to not only have kids but achieve your dreams too.

'I'm doing it for myself and I'm doing it to prove to (son) Sampson that if you've got a dream, don't let anyone tell you that you can't do it.'

Abby Connor (2:06.43) was fastest into the 200m butterfly final followed by Liz Dekkers (2:07.71).