Spain's Alba Vazquez Ruiz broke the women's junior world record in the women's 400 metres medley as action began at the 2019 International Swimming Federation (FINA) World Junior Championships in Budapest.
Vazquez Ruiz clocked a time of 4min 38.53sec in the final at the Hungarian capital's Duna Arena.
It bettered the previous mark of 4:39.01 set by Great Britain’s Rosie Rudin at the 2015 FINA World Junior Championships in Singapore.
Isabel Gormley of the United States finished second in 4:39.15, while Britain's Michaella Glenister came third in 4:39.35.
There was also a world junior record in the men's 4x100m freestyle relay final as the American quartet of Jake Magahey, Luca Urlando, Adam Chaney and Carson Foster touched home in 3:15.80.
Russia beat Italy by 0.03sec in the battle for the silver medal, posting a time of 3:16.26.
Among today's other winners was home favourite Gabor Zombori, who topped the men's 400m freestyle podium in a Championship record time of 3:46.06.
It improved his heat time of 3:46.97, which stood as a Championship record until the final.
Australia's Thomas Neill was the silver medallist in 3:46.27, while Russia's Aleksandr Egorov took bronze in 3:47.36.
In the women's 4x200m freestyle relay, the American team of Lillie Nordmann, Erin Gemmell, Justina Kozan and Claire Tuggle triumphed in 7:55.49.
Australia were 2.38 seconds behind in the silver medal position, while Canada were 5.65 seconds off the pace in third.
Four events ended at the semi-final stage today, with the finals tomorrow.
The top qualifier in the women's 50m breaststroke was Italy's Benedetta Pilato in 30.39.
American Josh Matheny led the way in the men's 100m breaststroke semi-final standings in 1:00.32, while Canada's Jade Hannah and Russia's Nikolay Zuev claimed the accolade in the women's 100m backstroke and men's 100m backstroke, respectively.
Hannah clocked a time of 59.97 and Zuev posted 54.08.
A total of nine medal sets will be awarded tomorrow.