Swimming star Ariarne Titmus shattered her fellow Australian Mollie O'Callaghan's world record in the women's 200 metres freestyle, clocking one minute, 52.23 seconds just weeks before the defence of her title at the Paris Olympics.

Titmus hit the wall at Australia's Olympic trials in Brisbane ahead of O'Callaghan, who also went under her previous world record of 1:52.85, finishing in 1:52.48 seconds.

"Looking at the results, it's unbelievable. I'm really happy to finally produce a swim in the 200 that I feel like my training reflects," said Titmus.

The Aussie pair will provide Hong Kong's Siobhán Haughey with stiff competition in the race for 200 metres glory in Paris, with O'Callaghan also expected to duel against Haughey in the women's 100 metres freestyle.

Titmus has been in top form in Brisbane, swimming the second-fastest 400 metres freestyle of all time on Monday as she also prepares to defend that Olympic title against the likes of Canadian Summer McIntosh and American star Katie Ledecky. (AFP)