Katie Ledecky won a record-breaking fifth straight 800m world title on Friday, just over an hour after Sarah Sjostrom surged to her fourth consecutive victory in the women's 50m butterfly.

Local hero Kristof Milak sparked delirium in the Duna Arena in Budapest when he grabbed the gold medal in the 100m butterfly, his second of the week.

The Australian mixed 100m freestyle team ended the evening by setting a world record in an event only added to the world championships in 2015.

Their time of 3min 19.38sec beat the record set by the United States in last World Championships in 2019 by 0.02sec. Canada were second, the Americans third.

Ben Proud claimed Britain's first gold of the championships as he grabbed victory in the 50m freestyle.

Australian Kaylee McKeown won the women's 200m backstroke for a first world title to go with three Olympic golds.

Ledecky led throughout the 800m as she took her tally of World Championship medals to 22, a record for a woman.

She finished in 8min 8.04sec to beat Australian Kiah Melverton by 10.73sec and Italian Simona Quadarella by 10.96sec.

Sarah Sjostrom takes a moment to enjoy her women's 50m butterfly gold at the  World Swimming Championships
Sarah Sjostrom takes a moment to enjoy her women's 50m butterfly gold at the World Swimming Championships AFP / Attila KISBENEDEK

"Year after year it's really hard work," said the 25-year-old American who won her first major title in the 2012 Olympics.

"In London I won my first gold 10 years ago, back then they said I was a one-hit wonder, and here we are, 10 years later and I have another gold.

"I'm so excited for the future as well. This was only my seventh fastest time in the last couple of years but after a long week the gold counts.

"Everyone's pushing me and I'm working on my stroke and these World Championships were tremendously exciting for me."

Sjostrom won her race in 24.95sec to edge Frenchwoman Melanie Henique by 0.36sec with China's Zhang Yufei third at 0.37.

"I had a lot of pressure on myself because of my past successes," said Sjostrom.

Sjostrom has 19 world championship medals, three behind Ledecky and is also chasing Michael Phelps' record of 10 World Championship butterfly medals set between 2001 and 2011. She has nine.

"Yes, I can do it," she said.

Kristof Milak waves after taking gold in the men's 100m butterfly final
Kristof Milak waves after taking gold in the men's 100m butterfly final AFP / Ferenc ISZA

"It feels unreal that I've been at this level for so long. I won my first title in 2009, Michael Phelps was still swimming at that time and I was really looking up to him."

Sjostrom fell on ice in Sweden in February 2021 and broke her elbow, but still won a silver in the Tokyo Olympics last July.

"It feels amazing to be here, to still be around and still be winning medals. It is not something I can take for granted."

Milak, who had already won the 200m butterfly title, delighted the home crowd at what he calls "my pool" as he finally won gold in the 100m. Caeleb Dressel, the reigning world and Olympic champion, pulled out of the competition on Wednesday.

"I missed him for sure, as you know I love good races, although this was also one," said Milak.

Milak won in 50.14sec, a comfortable 0.80sec ahead of Naoki Mizunuma of Japan, with Canadian Joshua Liendo a further three hundredths of a second back in third.

"I'm so proud to be Hungarian and I'm overjoyed that here in the arena 4,000 people were cheering for me," said Milak.

"I hope, in front of the TVs and all around the world, all 15 million Magyars gave me their support.

"I am so tired now, I can hardly wait for a rest."

In another event where Dressel was the reigning champion, Proud exploded from the blocks and held on to win in a time of 21.32.

American Michael Andrew was second on 21.41. Frenchman Maxime Grousset grabbed third.

"Great race, great field, great fans and great job!," said Proud.

McKeown chased American Phoebe Bacon down in the last lap to win at the touch by just 0.04sec.

"Everything turned out positively in the end," said McKeown.