PIX: Ledecky wins 19th gold; butterfly double by Milak

With her 19th FINA World Championships gold medal, Katie Ledecky is now within seven of Michael Phelps's all-time record.

Olympic champion Katie Ledecky stormed to a fifth straight 800m freestyle title at the swimming World Championships in Budapest on Friday while home favourite Kristof Milak added to his 200m butterfly crown with victory in the 100m butterfly.

Ledecky won in emphatic style, finishing more than 10 seconds faster than Australia's Kiah Melverton to seal her 19th gold medal at this level and go past Ryan Lochte.

The American is now within seven of Michael Phelps's all-time record.

Italian Simona Quadarella matched her performance from last year's Tokyo Games by securing a well-deserved bronze.

"It's just year after year of hard work. I think back to London and I made it the goal to not be a one-hit wonder, and here we are 10 years later," Ledecky told reporters.

"I'm happy with (the time), I kind of thought I'd be (8:0) 6 or 7, but to be 8.0 that's right there, and fastest I've been for a couple of years, so a really good end to a great week."

Earlier, Olympic silver medallist Milak, who smashed the 200m butterfly world record earlier in the week, moved clear of the field with 25 metres to go and barely looked troubled as he secured the win in 50.14 seconds.

Japan's Naoki Mizunuma came through in second in 50.94 seconds, finishing just ahead of Canadian Joshua Liendo Edwards.

Swede Sarah Sjostrom was also among the big winners as she continued her domination of the women's 50m butterfly for her fourth consecutive world title in the event and 18th individual medal overall.

The 28-year-old edged out France's Melanie Henique and Zhang Yufei of China for a place on the top of the podium.

In the women's 200m backstroke, there was heartbreak for American Phoebe Bacon after she was pipped to the title by Kaylee McKeown despite leading for much of the race.

The Australian won by 0.04 seconds while Bacon's compatriot Rhyan White was almost two seconds slower in third.

Australia were also dominant in the team events, with Jack Cartwright, Kyle Chalmers, Madison Wilson and Mollie O'Callaghan setting a new world record in the mixed 4x100m freestyle relay.

The quartet took gold ahead of Canada and the United States in 3:19.38, bettering the previous mark set by the Americans by 0.02 seconds.

"It's insane... I think we were always going to be hard to beat," said Chalmers.

Benjamin Proud earned Britain's first gold of the championships with victory in the men's 50m freestyle, leaning on a strong finish to prevail in 21.32 seconds. American Michael Andrew clinched silver while Frenchman Maxime Grousset came third.