The 16-year-old, a leading candidate for the US Olympic team at Beijing 2022, was forced to withdraw midway through the event in Nashville after contracting the virus.

At least two other athletes competing at the Championships - Brandon Frazier and Amber Glenn - have also tested positive for COVID-19.

Skaters at the event had to record a negative test result before their arrival, and were being tested again after four days.

"I am fully vaccinated, have been wearing a n95 mask and got two negative test results before leaving to Nashville," Liu posted on Instagram. 

"Things happen unfortunately...

"I am thankful to US Figure Skating for taking the extra precaution and having the necessary testing facilities to help keep everyone here as safe as possible. 

"I am feeling good physically and mentally."

Glenn said she had become "progressively slower, weak and sluggish", which she initially put down to pre-competition nerves and allergies before she tested positive.

Confirmation of the positive tests comes just days after COVID-19 breaches were discovered at the official US Figure Skating hotel for the competition.

USA Today reported seeing numerous maskless people at the hotel in Nashville, where many athletes, coaches, judges and officials are staying.

Masks and COVID-19 vaccination cards or tests are mandatory for all fans, while all three are required for members of the media at the trials, set to conclude tomorrow.