Australia's Kaylee McKeown has broken the 200 metres backstroke world record in Sydney ©Getty Images

Australia's triple Olympic gold medallist Kaylee McKeown has broken the 200 metres world backstroke record at the Sydney Olympic Aquatic Centre on a dramatic night at the New South Wales State Open Championships.

McKeown, came home in 2min 03.14sec  to eclipse the mark set by Regan Smith of the United States at the 2019 World Championships in Gwangju by 0.21 seconds.

She was not disturbed by a late switch to the time of the race, which began 20 minutes ahead of schedule.

McKeown set the pace from the start and turned at 29.34 after 50 metres, only 0.28 off the world record pace.

She reached the halfway mark in 1:00.73, still 0.36 outside world record time, but with 50m to go she turned for home at 1:31.84, precisely the same split as Smith had achieved four years ago.

McKeown's completed the last 50m in 31.30 to take her to the world record.

She had won Olympic gold in Tokyo at the distance and added world and Commonwealth Games gold medals last year.

She is now world record holder in both 100m back stroke and 200m backstroke in long course and also holds the best time for the distance in short course.

McKeown admitted it had been tough to re-motivate herself after winning three Olympic gold medals.

"After the Olympics I found it hard to get up behind the blocks again, but I’ve found a new love for the sport and it just goes to show that a happy swimmer is a fast swimmer," McKeown admitted.

"I haven't necessarily changed anything in my programme or training-wise. 

"It’s just that I’m happier."

Smith, her predecessor as world record holder, has put her degree studies on hold to concentrate on Paris 2024.

"I do love racing, it’s what we train for," McKeown continued.

"I knew it was going to be a new level heading into the Olympics and I think it’s great seeing Regan doing all her double ups.

"It’s scary and it’s daunting to me when you are looking at a competitor or competitors that fierce, the backstroke depth is definitely coming back at that top level so it’s exciting."