Canberra,  Ariarne Titmus has cemented herself as one of Australia's greatest Olympians with a gold medal in the 200m freestyle and a second victory over the reigning champion Katie Ledecky of the US at Tokyo 2020.

Titmus stormed home from third at the final turn in Wednesday morning's final in Tokyo to win the event in one minute and 53.50 seconds -- a new Olympic record.

Bernadette Haughey of Hong Kong took the silver in an Asian record time of 1:53.92, while Canadian Penny Oleksiak claimed the bronze in 1:54.70, with reigning Olympic champion Katie Ledecky fifth, reports Xinhua.

"It wasn't the time I wanted to swim but it's the Olympics and there is a lot going on. I don't want to ruin the rest of my meet by celebrating too hard but I'm very proud of what I've achieved," Titmus said after the race.

It comes just two days after Ariarne beat Katie in the 400m freestyle in one of the most anticipated races of the Games.

It was Australia's fourth swimming gold so far in Tokyo, making it one of the country's most successful Games in the pool in recent editions.

According to The Australian, Ariarne is just the third Australian to win the 200m and 400m double at an Olympic Games, joining Shane Gould and Ian Thorpe in achieving the feat.

Thorpe, a five-time Olympic gold medallist, praised Ariarne for sticking to her race plan after falling behind Bernadette.

"It is a remarkable performance and as we reflect on what Ariarne's been able to achieve, at the 100, I have to say I was a bit concerned at how far she was behind," he said.

"It was a great swim. To be able to back up from the 400m freestyle to deliver in the 200m freestyle is also part of this story," he added.

Born in the island state of Tasmania, Ariarne relocated to Queensland with her family at 14 for better training opportunities.

Prior to Wednesday's race, her father Steve shared experiences with other parents to help their children follow their sports dream.

"Maybe there is an opportunity to help other parents with the one percenter you have to provide to give the kids an opportunity," he told The Australian.

"They might be things like giving the chocolate section a miss at the shopping centre to go to the health food section, even though it might be dearer. If it's freezing cold or it's early in the morning and you don't want to take your kids to sport, make sure you do because kids dare to dream," he added.

Ariarne is next expected to make a podium finish in both 800m freestyle and 4x200m freestyle relay.