The American superstar clocked 8 minutes 8.04 seconds to finish more than 10 seconds ahead of Australia's Kiah Melverton to seal her fourth consecutive 400m/800m/1,500m triple at the event.

It was Ledecky's 19th gold at a worlds and her fourth this week, including the 4x200m freestyle relay.

"Really good end to a great week," Ledecky said.

Her 22 medals are the most for a female swimmer in world championships history. Only Michael Phelps, who won 26, has more.

Ben Proud won Britain's first gold of the championships, clinching the men's 50m freestyle in 21.32 - 0.09 ahead of American Michael Andrew and 0.25 ahead of France's Maxime Grousset.

"We're missing quite a few key players in the pool today," Proud said, referring to the absences of Caeleb Dressel, Florent Manaudou and Bruno Fratus.

"The whole podium from the Olympics last year wasn't in the final."

Dressel was due to race but withdrew from the worlds for unspecified reasons on Wednesday.

"It's not the same without him," Proud said.

"As soon as he was out, that quite changed the dynamics of the competition. A lot of people had a different type of pressure leading in.."

Dressel, the world record holder, was also missing from the 200 butterfly.

Kristof Milak followed up his win in the 100m butterfly - where he lowered his own world record - by adding the 200m.

The Hungarian swimmer delighted the home fans as he clinched the title in 50.14 ahead of Japan's Naoki Mizunuma and Canada's Josh Liendo.

Milak joined Phelps and South African Chad Le Clos as the only male swimmers to achieve the 100/200 butterfly double at a single worlds.

Sarah Sjostrom won her fourth consecutive 50m butterfly title, clocking 24.95 to head off Melanie Henique of France and Yufei Zhang of China for a record-equalling eighth gold medal in butterfly events at a worlds. Phelps now has to share his record.

American Torri Huske was sixth, 0.50 behind Sjostrom, who claimed her 18th individual medal at the worlds. Only Phelps, with 20, has more.

Australian Associated Press