US gymnast Jordan Chiles has lost her bronze medal in the Paris Olympics women's floor exercise after the Court of Arbitration for Sport ruled Saturday that the judging panel improperly granted an inquiry that moved her up from fifth.

As a result 18-year-old Romanian Ana Barbosu was awarded the floor medal by the International Gymnastics Federation (FIG) later on Saturday.

A devastated Chiles took to Instagram to post four broken hearts, adding: "I am taking this time and removing myself from social media for my mental health thank you".

US superstar teammate Simone Biles said: "Sending you so much love Jordan. Keep your chin up Olympic champ! We love you!"

In response to applications filed by the Romanian Gymnastics Federation and gymnasts Barbosu and Sabrina Maneca-Voinea, CAS ruled that the appeal of Chiles's degree of difficulty was submitted past the one-minute deadline for such inquiries and should not have been granted.

After the review, the score for Chiles, who won team gold with the United States, was upgraded to 13.766. That was enough to earn bronze behind Brazil's Rebeca Andrade and Biles.

But it was a devastating blow for Barbosu who thought she had bagged bronze with her score of 13.700.

Both she and Maneca-Voinea, who was pushed into fifth, departed the competition in tears.

"I can barely express my emotions, I can't believe it," Barbosu told Romanian media on Saturday after she was awarded her country's only medal in the gymnastics competition. 

"When I heard the news, I was afraid it wasn't true, and once I was sure, I hugged my parents and called everyone who had helped me."

Such scoring inquiries are regularly lodged during gymnastics competition, some are rejected and others are upheld, resulting in a change of score.

Romanian prime minister Marcel Ciolacu called it a "scandalous situation" and said he would boycott the Olympic closing ceremony.

The drama unfolded in the final event of gymnastics competition at Bercy Arena on Monday.

CAS said in its statement that its ruling applied to Chiles's score, which it said should be reinstated to its original 13.666.

But CAS didn't rule on the final floor exercise ranking, saying FIG would have to sort out the medals.

USA Gymnastics and the United States Olympic and Paralympic Committee issued a joint statement saying they were "devastated" by the ruling.

"The inquiry into the difficulty value of Jordan Chiles's floor exercise routine was filed in good faith and, we believed, in accordance with FIG rules to ensure accurate scoring," the governing bodies said.

"Throughout the appeal process, Jordan has been subject to consistent, utterly baseless and extremely hurtful attacks on social media.

"No athlete should be subject to such treatment. We condemn the attacks and those who engage, support or instigate them.

"We commend Jordan for conducting herself with integrity both on and off the competition floor, and we continue to stand by and support her."