The United States' Katie Ledecky won her 16th FINA World Championships gold medal in the women's 400m freestyle ©Getty Images

Two International Swimming Federation (FINA) World Championships records were set on the first day here by Katie Ledecky en route to a 16th gold medal at the event and French prospect Léon Marchand.

American Ledecky is a seven-time Olympic gold medallist, and travelled to Budapest as the most-decorated woman in the World Championships history with 15 victories to her name.

She made it 16 in the women's 400 metres freestyle final, clocking 3min 58.15sec.

Ledecky had been considered the strong favourite to win this race due to Australia's Olympic champion and world record holder Ariarne Titmus opting to focus on the Birmingham 2022 Commonwealth Games instead of the World Championships.

She emphasised her dominance in the heats, where she was the quickest performer by more than three seconds, and won the final by 1.24sec ahead of Canada's Summer McIntosh, the 15-year-old swimmer who collected her first medal on this stage.

Leah Smith of the United States rounded off the top three in 4:02.08.

Another World Championships record was set by 20-year-old Frenchman Marchand in the men's 400m individual medley.

He claimed a sensational victory in 4:04.28, with second-placed Carson Foster of the US finishing 2.28 further back.

Olympic champion Chase Kalisz of the US was also unable to keep pace with Marchand, taking third place in 4:07.47.

France's Léon Marchand won his first FINA World Championships medal in a record time for the event in the men's 400m individual medley ©Getty Images
France's Léon Marchand won his first FINA World Championships medal in a record time for the event in the men's 400m individual medley ©Getty Images

That was the same order as the top three in the heats, where Marchand also impressed with a 4:09.09 effort.

The other individual swimming medal of the day went to Australia's Elijah Winnington.

In a closely-fought battle with Germany's Lucas Märtens, it was Winnington who came out on top in 3:41.22, helped by a superb final 50m split of 26.50.

Mertens came through in second in 3:42.85, and Brazil's Guilherme Costa took bronze in 3:43.31.

Relay medals were also awarded today in the men's and women's 4x100m freestyle, both going to the reigning Olympic champions.

The US won the men's race in 3:09.34, which was 1.46 clear of Australia in second.

Third-placed Italy clocked 3:10.95.

Australia dominated the women's race, earning a 1.20 margin of victory over Canada with their time of 3:30.95.

The US came through in third in 3:32.58.

Earlier in the day, Japan's Yukiko Inui earned the first gold medal of the Budapest 2022 World Championships.

Her score of 92.8662 helped her to win the women's solo technical artistic swimming event at the Széchy Outdoor Pool on Budapest's Margaret Island.

Marta Fiedina of Ukraine placed second with 91.9555, while Greece's Evangelia Platanioti completed the podium after being awarded 89.5110 for her routine.

Swimming events at the FINA World Championships are due to continue tomorrow, with medals available in the men's 100m breaststroke and 50m butterfly, and women's 100m butterfly and 200m individual medley.

The duet technical final is also scheduled in artistic swimming.