US swim stars Caeleb Dressel and Katie Ledecky will target more gold in Tokyo on Saturday as Jamaica's Shelly-Ann Fraser-Pryce tries to become the first woman to win an individual Olympic athletics event three times.

Dressel, with two titles already under his belt this week, is widely expected to earn another in the 100m butterfly, where no other active swimmer has come close to his 49.50sec world record.

"I am well over the freestyle. I had a good prelim and semi of the fly, and I am looking forward to a good final tomorrow," said Dressel, already a winner in the men's 100m freestyle and 4x100m free relay.

Ledecky is the runaway favourite in the women's 800m free, winning gold at the last two Olympics and four straight world championships.

She holds the world record and heading into Tokyo owned the 24 fastest performances of all time in the event.

Kaylee McKeown is bidding to add the 200m backstroke gold, having upstaged American arch-rival Regan Smith to claim the 100m crown.

There is also the final of 4x100m mixed medley relay, a new Olympic event pitting men and women against each other.

On the track, Fraser-Pryce hopes to make it a treble of 100m golds, following her victories in 2008 and 2012.

Her compatriot Elaine Thompson-Herah is the defending champion in both the 100m and 200m, and likely to be pushing for another podium.

Caeleb Dressel is looking to add to his two Olympic gold medals won in Tokyo so far
Caeleb Dressel is looking to add to his two Olympic gold medals won in Tokyo so far AFP / Oli SCARFF

The final of the 4x400 relay, an event making its Olympic debut, will go ahead without the United States, who were disqualified for an illegal changeover.

A winner will also be crowned in the men's discus.

Switzerland's Belinda Bencic takes on Marketa Vondrousova of the Czech Republic for women's tennis singles gold.

Bencic has also reached Sunday's women's doubles final with Viktorija Golubic.

"To have a medal, it's the greatest thing. Even to be here as an athlete, in the Olympics, it's amazing," said Bencic, who could become the first Swiss woman to claim singles gold.

"I don't feel pressure right now. I just feel joy to have a medal."

Defending champions Brazil play Egypt in the quarter-finals of the men's football tournament, while Spain face Ivory Coast.

Li Junhui and Liu Yuchen can give China a second badminton gold in the men's doubles final, while New Zealand, Fiji, France or Britain will be crowned in the women's rugby sevens.

Day eight features a total of 21 gold medals, including in archery, fencing, judo, sailing, shooting, trampoline gymnastics, triathlon and weightlifting.