China's Ye Shiwen competes in the women's 200m individual medley heats.
China hit back at doping claims concerning star swimmer Ye Shiwen on Tuesday as Michael Phelps aimed to become the most decorated Olympic athlete in history.
Teenage star Ye has been besieged by thinly-veiled allegations of doping since her world record-breaking victory in the 400m medley final, with top American coach John Leonard branding her performance "impossible."
However China's authorities went on the offensive at Ye's critics on Thursday, while a slew of Olympic swimming greats, coaches and officials also lined up in support of the 16-year-old sensation.
"The Chinese athletes, including the swimmers, have undergone nearly 100 drug tests since they arrived here," Jiang Zhixue, the head of anti-doping at China's General Administration of Sport, told Xinhua news agency.
"Many were also tested by the international federations and the British anti-doping agency. I can tell you that so far there was not a single positive case.
"I think it is not proper to single Chinese swimmers out once they produce good results. Some people are just biased."
Australian swimming great Ian Thorpe insisted that the large improvements Ye had made to her personal best in the past year were not unusual.
"We have to remember that young swimmers can take chunks of time off that other people can't," Australian swimming legend Ian Thorpe told the BBC.
Former British swimmer Adrian Moorhouse, a gold medalist in the 100m breaststroke in the 1988 Seoul Games, issued a strong defense of Ye, saying it was possible China had unearthed their own Michael Phelps.
"I think it's sour grapes," Moorhouse said when asked about Leonard's comments. "I think it's quite insulting actually."
Ye will attempt to win her second gold of the Games later Tuesday when she lines up in the 200m medley final, an event she won at the World Championships in Shanghai last year.
Phelps, meanwhile, can make Olympic history by winning two medals of any colour in the pool in the evening.
The American goes in the 200m butterfly final which he has won for the last two Olympics and then will join his US team-mates as they defend their 4x200m freestyle relay.
Phelps, 27, is having a rollercoaster Games after slumping to a shock fourth in the 400m individual medley dominated by his fellow American Ryan Lochte and then had to settle for silver in the 4x100m freestyle relay.
That medal took Phelps' Olympic career total to 17, leaving him just one short of the all-time biggest career haul of 18 won by Soviet gymnast Larisa Latynina.
France's Camille Muffat and US teen sensation Missy Franklin go head-to-head in the women's 200m freestyle final as they both attempt to win a second gold of these Games, although Franklin must do so from lane eight.
In the gymnastics, China's hopes of emulating the success of their men's team by retaining the team title appear slim after they were outclassed by the United States in qualifying.
US superstars Kobe Bryant, LeBron James and their star-studded ensemble cast are expected to crush minnows Tunisia in their second match of the basketball tournament.
After easing past France in their opener, the Americans looked ominously determined to prove they are superior to the original Dream Team which lit up the 1992 Barcelona Olympics.
The first of 15 gold medals up for grabs on Tuesday was won by defending champions Germany in the equestrian three-day eventing.
Great Britain finished second to earn a silver medal for Queen Elizabeth II's granddaughter Zara Phillips, with New Zealand claiming bronze.
Meanwhile, Saudi Arabia judoka Wojdan Shaherkani was given the go-ahead to fight at the Olympics after a row over the wearing of a hijab was resolved, the International Olympic Committee confirmed.
The Saudis had threatened to pull the fighter out of the Games if she was forced to compete with her head uncovered before a compromise was found.