Japan's Naomi Osaka, star of the Tokyo Olympics' opening ceremony, returns from her self-imposed tennis exile on Sunday as US legend Simone Biles sets about equalling the all-time record for gymnastics gold medals.

Australian Open champion Osaka has not played since May, when she walked out of Roland Garros saying that media commitments were harming her mental health.

But she appeared buoyant after lighting the Olympic cauldron on Friday, and will expect a warm welcome in Tokyo even if fans are barred because of coronavirus restrictions.

Firing up the cauldron was "undoubtedly the greatest athletic achievement and honor I will ever have in my life", tweeted Osaka, who plays China's Zheng Saisai in the first round.

Other highlights on day two, with 18 gold medals in play, include the men's 400m individual medley swimming final, after Japanese world champion Daiya Seto's shock exit in the heats, and the women's final featuring Hungarian medal machine Katinka Hosszu.

The first Olympic skateboarding champion will be crowned, with America's Nyjah Huston and Japan's Yuto Horigome fierce rivals in the men's street competition, while surfing also makes its Games debut.

A formidable USA team led by Kevin Durant take on France in basketball, and Dutch two-time world champion Anna van der Breggen will target back-to-back golds in the women's cycling road race.

Japanese tennis player Naomi Osaka lit the Olympic cauldron
Japanese tennis player Naomi Osaka lit the Olympic cauldron AFP / Franck FIFE

The Ariake Gymnastics Centre will be the setting as Biles, 24, starts her bid to become the first woman in more than half-a-century to retain the all-around title.

The American could leave Tokyo with a career haul of nine Olympic gold medals, equalling the record set by Soviet gymnast Larisa Latynina in Tokyo in 1964.

Biles has not lost an all-around competition since 2013, an eight-year era that has encompassed 19 world championship titles and four Olympic golds.

In acknowledgement of her domination, Biles has become the first athlete to be awarded their own emoji on Twitter: a goat in a leotard symbolising her status as the G.O.A.T., or greatest of all time.

"I just hope that kids growing up watching this don't or aren't ashamed of being good at whatever they do," she said in a recent interview.

The inaugural men's surfing could be spectacular with a tropical cyclone set to whip up big waves at Tsurigasaki Beach, 100 kilometres (60 miles) west of Tokyo.

Brazil's Italo Ferreira, who learned to surf standing on the foam boxes his father sold fish from, will start as one of the favourites.

"Each victory gives you a lot of grit, a lot of perseverance, that makes you more professional and gives you more desire to win," the 2019 world champion told AFP.