US gymnast Simone Biles has pulled out of the women's gymnastic all-around event.

USA Gymnastics posted a statement to Twitter saying: "After a further medical evaluation, Simone Biles has withdrawn from the final individual all-around competition at the Tokyo Olympic Games, in order to focus on her mental health.

"Simone will continue to be evaluated daily to determine whether or not to participate in next week's individual event finals.

"Jade Carey, who had the ninth-highest score in qualifications, will participate in her place in the all-around.

"We wholeheartedly support Simone's decision and applaud her bravery in prioritising her wellbeing. Her courage shows, yet again, why she is a role model for so many."

The American superstar sparked concerns on Tuesday night when she pulled out just minutes into the women's team gymnastics final in Tokyo.

Biles is a star on the vault – the place Biles has gone where nobody ever has before with the incredible Yurchenko double pike – but the four-time gold medallist baulked on her first attempt.

Simone Biles competes on the balance beam during the women's US Olympic Gymnastics Trials earlier this week. (Photo / AP)

The bizarre incident meant she only completed 1.5 rotations instead of 2.5 and failed to stick the landing. Biles was clearly irked and grimaced on her way back, earning a 13.766 — the lowest score of all six American and ROC (Russian Olympic Committee) competitors.

USA Gymnastics later confirmed Biles would not play any further part in the final.

"Simone has withdrawn from the team final competition due to a medical issue," a statement said. "She will be assessed daily to determine medical clearance for future competitions.

"Thinking of you, Simone!"