The United States swept five golds to top the medals table on Thursday while a Chinese swimmer had tested positive at the Rio Olympics.
Chen Xinyi, 18, tested positive for hydrochlorothiazide, a diuretic, on Aug. 7 after she finished fourth in the 100m butterfly final in 56.72 seconds, the Chinese Swimming Association (CSA) announced in its statement on Friday morning.
Chen has applied to the International Olympic Committee (IOC) for testing of sample B and a hearing to look into the matter, said the CSA.
"The CSA has taken this matter seriously and demanded full cooperation from Chen in the investigation," the CSA said in the statement.
"The CSA resolutely opposes use of banned substances. We will cooperate with the Court of Arbitration of Sport during its investigation and will respect the final ruling by the CAS."
Led by superstar Michael Phelps, the U.S. swimmers contributed three out of the five gold medals pocketed by the U.S..
To a thunderous crowd, Phelps stormed to the gold medal in the men's 200m individual medley and became the first swimmer to win the same event at four consecutive Olympics.
Earlier at the Olympic Aquatics Stadium, Ryan Murphy grabbed his second gold medal of the Rio Olympics, winning the men's 200m backstroke final while Simone Manuel and Penny Oleksiak of Canada have tied for the gold medal in the women's 100m freestyle.
"My first gold medal, at my first Olympics, is kind of a surprise to me. I never thought I would be in this position but I'm so blessed and honored on the medal stand," said Manuel.
"All my hard work has paid off and I'm really happy about it. Team U.S.A is awesome. We're a family and it's a great support system," the 20-year-old American added.
Besides, U.S. star gymnast Simone Biles took women's all-around title without meeting any challenge. The three-time all-around world champion took the gold medal with a total score of 62.198 points.
Coming to Rio with three all-around world titles in a row and a total of 10 gold medals from the World Championships, Biles has been the odds-on favorite in many events at the 2016 Olympic Games.
"I'm very excited and relieved, I've finally done it. You never know the feeling until it hits you," said Biles, who became the first reigning world champion in the women's individual all-around to claim the Olympic title in the same event since 1996, when Lilia Podkopayeva from Ukraine triumphed.
Elsewhere, U.S. judoka Kayla Harrison won back-to-back Olympic titles in women's 78kg event.
China only bagged one gold medal as world number one Ma Long defeated Zhang Jike in the final to win the table tennis men's singles gold.
With the victory, Ma completed his Grand Slam request and came out as the fifth male paddler to do so in table tennis after winning an All-Chinese final over defending champion Zhang.
It has been China's 11th gold at the Rio Games, while Zhang added a silver.
Zhang, already a Grand Slam winner four years ago after crowned at the World Championships, World Cup and Olympic Game in just 15 months, made too many unforced errors and failed to perform his trademark backhand to easily surrender.
In fencing, Romania beat top-ranked China to win the gold medal in women's epee. It's the first medal of the Rio Games for the Romanians, who outscored China 44-38.
At the Lagoa Stadium, Germany snatched two golds from the men's and women's quadruple sculls in the rowing regatta.
Brothers Martin Sinkovic/Valent Sinkovic from Croatia lifted the title in the men's double sculls while in the lightweight men's four, world championship silver medalists Switzerland took the gold.
Fiji harvested the first ever Olympic gold as its men's rugby sevens team trounced Britain 43-7 in a lopsided final.
It is first Olympic gold medal for Fiji and also the first ever Olympic medal for the island country known for its athletic rugby.
After Thursday's finals, the United States leads the table with 16 golds, as China and Japan were at second and third on 11 and 7 golds respectively.
