Titmus books ticket to Paris Olympics with second fastest 400m in history

The 23-year-old went within 0.06 seconds of breaking her own world record as she dominated the 400-metre freestyle on the opening night of finals at the Australian Swimming Trials.

Although Australia's Olympic team will be confirmed on Saturday night, the performance assures Titmus a place with further opportunities to come over 200m, 800m and relays.

"It's a nice feeling to finally say 'I'm going'. It's nice to actually have the box ticked," she said.

"It's a funny feeling having your PB (personal best) as the world record. Six 100ths off is a great swim for me and I don't want to be breaking world records here I want to be breaking world records when it matters on the international stage. (But) that gives me good confidence for six weeks' time."

Roared on by a crowd at Brisbane Aquatic Centre not far from where she now lives, the Launceston-born freestyle phenomenon was on course to better her 3:55.44 world record for all but the final few metres.

"After this morning, I thought there was a chance [of breaking the record]," Titmus said.

"The goal isn't to swim my best here, the goal is to book a ticket [to the Olympics], so I'm excited to see what I can do in Paris. I think I've timed my prep perfectly."

The former Riverside and Launceston Aquatic swimmer, who now represents St Peters Western, clocked 3:55.44 to lead home Lani Pallister (4:02.27) and training partner Jamie Perkins (4:04.38).

"Trials is a bit of a free shot for me," Titmus added.

"I don't have to worry about getting under a qualifying time, so if I stuff up, I have the luxury that I'd probably still be on the team.

"So it's about trying new things and to win, you always have to try new things. You can't just expect to do the same thing and keep winning.

"I haven't seen my splits but if I'm that far under, I think that gives me confidence that I took it out and I was quite fearless."

Titmus, whose family moved from Launceston to Brisbane in 2015, had earlier clocked 4:01.57 to cruise into the final as the fastest qualifier.

The three-time Tasmanian athlete of the year won gold medals in the 200 and 400m freestyle at her first Olympics in Tokyo plus a silver medal in the 800m and bronze in the 4x200m freestyle relay.

She has recorded six of the top 10 fastest times ever over 400m. Three of the others were set by Katie Ledecky and the pair's impending showdown is being billed as one of the biggest events of the Paris program.

The Olympic Games begin on July 24 with the swimming schedule getting underway three days later and the women's 400m final one of four medals to be decided on the opening night.