Aust women smash record to win gold

Australia's women have set a sizzling pace at the world short course swimming championships in Melbourne with the relay team smashing a world record and Lani Pallister also winning gold.

The Australians - Mollie O'Callaghan, Madi Wilson, Meg Harris and Emma McKeon - set a 4x100m time of three minutes 25.43 seconds to eclipse the Dutch mark of 3:26.53 from 2014.

Superstar McKeon swam the first sub-50 second 100m freestyle split by a woman with a 49.96 seconds to overhaul the Americans, who also beat the previous world record mark, to secure the gold medal.

Italy also set a world record in the men's 4x100m relay to cap a red-hot first night of racing.

The Italians touched the wall in 3:02.75, beating the previous mark of 3:03.03 set by the American men in 2018.

Australia finished second in 3:04.63.

McKeon, who won the 50m and 100m freestyle in Tokyo amongst her haul of 11 Olympic medals, was in another class as she powered the home team from third place into the winning position.

The victory completes a treble for the Australian women, who also own the Olympic and world titles in the event.

With $3 million prize money on offer, the Australians also collected $37,000 for breaking a world record.

McKeon, who had to make up almost a second, said she was confident she could close the gap.

"I thought I could - the other teams may have had a really good front end and we knew that we had a good team put together," the 28-year-old said.

"To come away with a world record is pretty good.

"I put my best races together in a relay, I love the team event so I'm very happy to do that on the first night."

Pallister made the most of the absence of world champion Li Bingjie to win Australia's first gold medal of the night in the 400m freestyle.

World record holder Li was a shock absentee on the opening day of racing with Chinese media reporting she had a fever.

Australian star Ariarne Titmus, who Li took the record from, also skipped the meet.

The daughter of former Australian distance swimming great Janelle Elford, Pallister qualified second fastest into final behind Kiwi Erica Fairweather.

But Pallister turned the tables in the final, powering home in three minutes 55.04 seconds.

The 20-year-old has had a horror run with injury and illness over the past 18 months, undergoing heart surgery as well as battling an eating disorder and glandular fever.

She wasn't thrilled with her time but was delighted to have won gold with her mum in the stands after almost giving the sport away.

"I pretty much gave this sport away at the end of last year - I hadn't trained for close to three months and didn't really want anything to do with it anymore," Pallister told reporters.

"It was more that I lost my love for the sport as I'd missed four senior teams in a row by one spot, which when you're that close constantly, it's just kind of like breaks your heart one by one. 

"So to be in the position that I am at the moment ... now competing here at short course with a gold medal is just insane."

Triple Olympic gold medallist Kaylee McKeown swam a personal best but had to settle for bronze in the 200m individual medley final behind Americans Kate Douglass and Alex Walsh.

World record holder in the long course 100m backstroke, McKeown managed to best her own Oceania record by 0.11 seconds with a time of 2:03.57.

The 21-year-old had to back up an event later in the 100m backstroke semi-final and progressed through to the final after placing second behind Canadian Ingrid Wilm.

Teen star O'Callaghan will enter the medal race as the fastest in the field, winning the other semi.

Isaac Cooper, making his return to the Australian team after being sent home from the Commonwealth Games training camp for misusing prescription medication, edged into the men's 100m backstroke final in seventh spot.

In other results, South African Matthew Sates won the 200 individual medley and Italian veteran Gregorio Paltrinieri took gold in the men's 1500m.