Three swimming world records have been broken on the first day of competition in Rio.

Briton Adam Peaty beat his own world record in the men's 100m breaststroke, with a time of 57.55 seconds.

After repeated frustration on sport's biggest stage, Hungarian Katinka Hosszu crushed the women's 400m individual medley record to make her first Olympic medal gold.

Hosszu, known as the "Iron Lady" for her gruelling schedule, had captured nine medals - including five golds - at the world championships but never won an Olympic medal.

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She defiantly pumped her chest before breaking into a huge smile.

She had led all the way and touched in 4:26.36, easily eclipsing the record of 4:28.43 held by China's Ye Shiwen.

And Australia's 4x100m women's freestyle relay team of Emma McKeon, Brittany Elmslie, Bronte Campbell and sister Cate Campbell defended their country's title in the event, clocking a time of three minutes 30.65 seconds.

The Campbells carried their squad to victory, with Bronte, the younger of the sisters, snatching the lead from American Dana Vollmer on the third leg and Cate pulling away from Vollmer's team-mate Katie Ledecky on the final down-and-back.