Katie Ledecky has eye on more milestones ahead of Leon Marchand show

There was also drama at La Defense Arena as a Slovakian swimmer collapsed after her morning heat in the 200m individual medley.

The 21-year-old Tamara Potocka was taken away from the pool on a stretcher with an oxygen mask on her face. She was conscious and under medical assessment, a venue official said.

American Ledecky has already shredded the record books in Paris, becoming the most decorated female swimmer at Olympics with a 13th medal on Thursday when she helped the United States to silver behind Australia in the women's 4x200m freestyle relay.

On Saturday, she can reset another clutch of records after topping the timesheet for the 800m final with a swim of eight minutes, 16.62 seconds, 1.86 seconds better than compatriot Paige Madden.

Victory would give her a ninth Olympic gold medal, drawing her level with former Soviet gymnast Larisa Latynina's record haul for a female Olympian from any sport.

Ledecky can also become the first woman to win four Olympic golds in the same swimming event and only the second swimmer to pull off the feat.

Fellow American great Michael Phelps won four 200m individual medley golds from Athens 2004 through to Rio 2016.

However, the 27-year-old said she was only focused on the task at hand.

"I've tried not to really think about it," she said of the history.

"I'm just taking it one event at a time and I know I have challenges in each of my events."

Another swimmer chasing history is home hero Marchand whose bid for the 200 IM title and fourth Olympic gold of the meet will be appointment viewing for the host nation.

In one Games, Marchand can move to equal second on the all-time list for Olympic golds in individual events, joining a select group of swimmers including Mark Spitz and Alexander Popov.

Only Phelps, with 13 individual golds, has more.

Summer McIntosh will also put her name among the greats if she wins a third individual gold in the women's 200m IM.

McIntosh was fastest into the evening semi-finals with a time of 2:09.90.

Defending champion and world record holder Caeleb Dressel eased into the 100m butterfly semi-finals with the sixth-fastest time in the heats.

Hungary's Kristof Milak, runnerup behind Dressel at Tokyo in the event, was fastest in 50.19 seconds.

But Phelps' old butterfly rival Chad le Clos crashed out with the 24th fastest time, the South African blaming a muscle injury in his upper back after a training mishap.

The US team took the top seed for the final of the 4x100m mixed medley ahead of Australia and China.

There will be two other golds on offer before Marchand goes for the 200 IM title in the evening session.

Dressel will defend his 50m freestyle crown in a race with former world champions Cameron McEvoy and Ben Proud.

McEvoy and Proud advanced to the final with the equal fastest times in the semis but Proud was awarded lane four, which is reserved for the quickest qualifier.

Australia's defending champion Kaylee McKeown, already the 100m backstroke winner, will go for another individual gold in the 200m backstroke later on Friday.

Victory would make her the first women's swimmer to complete the Olympic backstroke "double-double" by retaining both her titles.