Biles in Olympic spotlight as Bermuda win first ever gold

History-chasing gymnastics superstar Simone Biles goes for her first gold medal of the Tokyo Games on Tuesday after Flora Duffy delivered Olympic glory for tiny Bermuda for the first time.

Home favourite Naomi Osaka is also in action as she pursues her challenge for a tennis gold medal for Japan, who topped the medals table heading into the fourth day of the Tokyo Games.

Organisers are nervously monitoring the progress of Tropical Storm Nepartak that is expected to make landfall in northeastern Japan during the day, forcing the rescheduling of rowing and archery.

Gold medals are up for grabs in the first-ever Olympic surfing competition after the final day was brought forward due to the approaching storm.

Triathlete Duffy won the first gold of the day in the women's event, making Bermuda the smallest territory or nation in terms of the population -- around 70,000 -- to win a gold medal at a Summer Games.

The 33-year-old timed 1hr 55min 36sec to come home more than a minute ahead of Britain's Georgia Taylor-Brown, with American Katie Zaferes taking the bronze.

The focus in the morning will be on events in the pool, including the men's 100m backstroke, which features US world record holder and defending champion Ryan Murphy.

Later, all eyes will be on Biles at the Ariake Gymnastics Centre as the 24-year-old four-time Olympic champion seeks to erase the memory of an uncharacteristically error-strewn qualifying competition.

- Biles pressure -

Biles made mistakes on floor and vault in the women's team competition on Sunday and the other Americans followed suit as they failed to post the top score of the day for the first time at a world championship or Olympics since 2010.

The US women came to Tokyo as firm favourites but Biles admitted to feeling the pressure in an Instagram post on Monday, saying "I truly do feel like I have the weight of the world on my shoulders at times."

With spectators banned from the gymnastics and most events at the Games to protect the Japanese public from coronavirus, Biles does not have a crowd to inspire her.

But it would be a huge shock if she failed to win a fifth gold to kick off her attempt to equal or surpass Soviet great Larisa Latynina's record of nine gymnastics titles.

Osaka, one of the faces of the Games after lighting the cauldron at the opening ceremony, takes on 2019 French Open finalist Marketa Vondrousova of the Czech Republic in the third round.

With the competition between swimming superpowers the United States and Australia intensifying, American great Katie Ledecky has to navigate a 200m semi-final in the morning before trying to recuperate for Wednesday's 1500m final.

Ledecky came up short in the first part of her medal quest in Tokyo when Australian arch-rival Ariarne Titmus beat her to gold in the 400m freestyle on Monday. Ledecky is also swimming the 800m freestyle and possibly a relay.

Japan won three gold medals on Monday to move to eight overall, one ahead of the USA and two ahead of China.