Leisel Jones unleashed her fastest 200m breaststroke in Australia at the national age swimming titles in Brisbane on Tuesday night.

Jones clocked 2minutes 25.57seconds to be just 0.11s off her career best of 2:25.46 set during the 2001 world championships in Fukuoka, Japan.

The 17-year-old took the race out hard to be just off world record pace at the halfway mark but she slowed to finish more than two seconds off Chinese swimmer Hui Qi's two-year-old world record of 2:22.99.

She finished about six metres ahead of the rest of the field in the girls' 17-18 years event.

Coach Ken Wood is so convinced of Jones's ability, when asked about her world record prospects he consistently replies: "It's not a matter of if, it's when".

Jones said she'd been practising taking the race out hard to get a feel for the pace she needs to generate for a world record assault.

"Ken's always told me I have to practice getting out there and sort of trying to hold on," she said.

"My back end's obviously not as good as the world record is. I'm just working on that."

She's embarked on an ambitious weights program in a bid to improve her strength, leg-pressing up to 320kg at a time.

The age championships is where it all began for Leisel, who emerged at the 2000 titles in Perth as a 14-year-old, ahead of the Sydney Olympics.

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