Mollie O'Callaghan falls agonisingly short of record-breaking World Championships gold

Australian swimmer Mollie O'Callaghan has won silver in the Women's 100m freestyle at the World Aquatics Championships in Singapore.

She finished just 0.12 seconds behind the winner, Marrit Steenbergen, from the Netherlands, who won with a time of 52.55.

A win for O'Callaghan would have put her one ahead of Ian Thorpe as the Australian all-time leading gold medal winner at the world swimming championships.

But at the end of a busy program in which she's won three gold medals, fatigue has caught up to her.

The first thing she said to journalists post-race was: "Tired, very tired."

"I think coming off last night, and especially — like I've said a thousand times — I haven't had the greatest prep towards this, and to do what I did tonight and last night and the night before, I'm pretty proud," O'Callaghan said.

"To be on the podium is something special, and I'm always grateful for it.

"Obviously, we'd love to win, everyone would love to win, but like that's all I could do tonight, so I'm pretty happy."

She said she had the heaviest program in the Australian team, but with two relays still to come, she still has a chance of pulling ahead of Thorpe's record.

Australia's Men's 4x200m freestyle relay team of Flynn Southam, Charlie Hawke, Kai Taylor and Max Giuliani continued a successful campaign for the Dolphins, coming third behind Great Britain and China.

Southam, Taylor and Giuliani added bronze to the gold medals on night one of the championships in the 4x100m freestyle relay.

"We've come away with a bronze and we're such a young team," Giuliani said.

"I think we're all a real threat in the future — we're all 20, 22, 21, we've got a lot left in us.

"I think come 2028, we're going to be a real force to be reckoned with."

Cameron McEvoy qualified fastest after the semifinals of the men's 50m freestyle.

His time of 21.3 seconds equalled his time at the Australian trials as the fastest time recorded in the world this year.

Normally, 50m freestylers don't take a breath, but McEvoy did with about 10 metres to go, suggesting he can go faster.

"[It] suggests I'm in pretty good shape," McEvoy said.

"Sprinting at these speeds, it's difficult because sometimes taking your foot off the gas allows you to hold speed a little bit better than gripping it too hard.

"It's a completely new race tomorrow, it's going to be hard."

He said his main priority after winning the Olympic gold medal at Paris last year was swimming as fast as he possibly could, rather than winning.

"For me now, primarily, I'm after a time," he said.

"Always like to get my hand on the wall first, but I think most of the passion comes from chasing that time — that perfection," McEvoy said.

Kaylee McKeown qualified fourth fastest for the women's 200m backstroke final as she seeks to add to the 100m final she won against the odds earlier in the week.

Matthew Temple made it through to the finals of the men's 100m butterfly final in sixth spot.

Two Australians qualified for the final of the women's 50m butterfly: Alexandria Perkins, who won bronze in the 100m butterfly, qualified fourth, and Lily Price was seventh fastest.

The United States and Australia both have five gold medals, but the US leads the medal table with 20 overall compared to Australia in second with 13.