Australia's Ariarne Titmus has won her second gold medal in three days, breaking the world record in the women's 400m freestyle at the world short-course swimming titles in China.

Key points: This year the young Tasmanian became the first woman in 36 years to win the 400-800m freestyle double at the Commonwealth Games

This year the young Tasmanian became the first woman in 36 years to win the 400-800m freestyle double at the Commonwealth Games In other Australian results on day four in Hangzhou, Holly Barratt won a silver medal in the women's 50m butterfly

In other Australian results on day four in Hangzhou, Holly Barratt won a silver medal in the women's 50m butterfly The Australian team of Cameron McEvoy, Cameron Jones, Grayson Bell and Louis Townsend came fourth in the 4x50m freestyle relay

The 18-year-old finished the race in a new world record time of three minutes 53.92 seconds in Hangzhou overnight, backing up from her win earlier in the week in the 200m freestyle.

She won by more than half a second in front of home favourite Wang Jianjiahe, beating the Chinese swimmer's existing world mark by 0.05.

Titmus went out fast, and held her lead all the way through the race.

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The young Tasmanian extended her gap over Jianjiahe to nearly a second with 50m to go, and although the home crowd roared her home, she was unable to get closer than 0.64 seconds in the end.

Jianjiahe's teammate, Li Bingjie, came third in a time of 3:57.99, with American Leah Smith — who won the event in 2016 — fourth in 3:58.58.

"I am a little bit in shock. I knew the Chinese girl would go out fast and I was worried she would have a little left in the tank at the end, but I held her off," Titmus said.

Titmus is already Australia's undisputed long course distance queen after becoming the first woman in 36 years to win the Commonwealth 400m-800m freestyle double at the Gold Coast in April.

After she won the 200m freestyle on Wednesday in a new Australian and Oceania record time of 1:51.38, Titmus's coach Dean Boxall said they had been focusing on her speed in the lead up to the six-day event, held in a 25m short-course pool.

Titmus has now proven herself a master of both speed and distance in the pool.

Ariarne Titmus (R) beat Leah Smith (L), who won the event in 2016. ( AP: Ng Han Guan )

"I put in a lot of hard work since our trials five weeks ago and the turnaround I have had in that time is unbelievable. I dropped six seconds off my 400 and that shows what training hard can do," she said.

"I can't believe it, and for it to be a short course world record is something. I am someone who does not pride themselves on speed, but I will take it."

In other Australian results on day four in Hangzhou, Holly Barratt won a silver medal in the women's 50m butterfly in a time of 24.80, behind champion Ranomi Kromowidjojo of the Netherlands (24.47).

Emily Seebohm was trying for a third straight podium at the titles in the women's 100m individual medley, but she finished sixth behind Hungary's Katinka Hosszu, who won in a time of 57.26.

The win was Hosszu's third gold medal for the championships, after she earlier took out the 200m butterfly and 400m individual medley events.

The Australian team of Cameron McEvoy, Cameron Jones, Grayson Bell and Louis Townsend came fourth in the 4x50m freestyle relay behind winners the United States.

McEvoy came sixth in the 50m freestyle final (21.02) behind gold medallist Vladimir Morozov of Russia.

In the men's 4x200m freestyle relay final, the Australian team — Alexander Graham, Jack Gerrard, McEvoy and Thomas Fraser-Holmes — finished fifth behind the winning team from Brazil.

AAP/ABC