Australia and Italy both earned places in the history books with new relay world records on day one of the Short Course World Swimming Championships in Melbourne.

The Australian 4x100m freestyle relay team - led by trailblazer Emma McKeon - found themselves trailing the USA for 350m but stormed back to take the world title in front of the home crowd.

Helped by the first-ever sub-50 split from McKeon, who clocked 49.96 seconds, Australia posted a world-record time of 3:25.43 to claim the gold medal ahead of the USA.

The silver medal-winning USA team earned an American record of their own with a total time of 3:26.29, while the Canadian team posted 3:28.06 for a new national record.

Great Britain, meanwhile, finished in seventh with 3:33.47 on the clock, and there was a second relay world record in the men's 4x100m event courtesy of the Italian quartet.

There would be no one-two for Australia in the freestyle relay events, as Alessandro Miressi (46.15), Paolo Conte Bonin (45.93), Leonardo Deplano (45.54), and Thomas Ceccon (45.13) earned their pages in the world record books.

Italy clocked an overall world record time of 3:02.75 to be crowned world champions for the first time since 2006, as the USA's record of 3:03.03 - set in 2018 - was surpassed.

Australia still took the silver medal with an Oceanic record of 3:04.63, as the USA secured the third and final spot on the podium with a bronze-medal worthy time of 3:05.09.

Elsewhere on day one, another Australian gold medal went to Lani Pallister in the opening women's final - the 400m freestyle - with the 20-year-old finishing in 3:55.04.

Eighteen-year-old Erika Fairweather (3:56.00) pushed Pallister all the way and was rewarded with the silver medal, while bronze medallist Leah Smith of the USA was further back in bronze with 3:59.78.

In the men's 1500m freestyle, Italy's Gregorio Paltrinieri stormed to the gold medal with a time of 14:16.88, as France's Damien Joly (14:19.62) and Norway's Henrik Christiansen (14:24.08) placed second and third respectively - GB's Daniel Jervis posted 14:30.47 to finish sixth.

The women's and men's 200m medley titles were also decided on day one, where South Africa's Matthew Sates set a new African record of 1:50.15 to win the men's title, while Kate Douglass also broke the American record in the women's event with 2:02.12 to finish first. body check tags ::