Leon Marchand demonstrated again on Friday why many consider him the best swimmer of his generation as he stormed to his fourth individual gold medal in the pool at La Defense Arena.

The French star took command on the backstroke leg of the men's 200m individual medley and never looked back, winning in an Olympic record time of 1 minutes, 54.06 seconds.

Britain's Duncan Scott won his second straight silver in the event while defending champion Wang Shun of China settled for bronze.

Marchand is the first French athlete to take four individual golds, as opposed to team ones, at a single Summer Games and only the third male swimmer to do so after Americans Michael Phelps and Mark Spitz.

"It's incredible, it was really magical," the 22-year-old told French TV. "The whole stadium was fully behind me and I took advantage of it. It enabled me to win four medals."

It was a good night for Australia as the Dolphins came away with two more gold medals from the meet.

Kaylee McKeown cemented her place among the greats of Olympic swimming on Friday as she became the first woman to retain both of the backstroke titles with gold in the 200m event in Paris.

The 23-year-old world record holder once again overhauled American challenger Regan Smith in a battle royale to claim the win in an Olympic record of 2 minutes, 3.73 seconds.

Smith took silver, 0.53 seconds behind her Australian nemesis.

Kylie Masse took bronze for Canada.

Meanwhile, Australia's Cameron McEvoy took his first Olympic gold medal when he won the men's 50 metres freestyle.

Britain's Ben Proud took the silver medal, and France's Florent Manaudou the bronze - 12 years after he won gold at London 2012.

Defending Olympic champion Caeleb Dressel of the United States finished sixth.

McEvoy is the first Australian man to win the shortest distance on the programme. (Reuters)