A US coach yesterday described the incredible record-breaking performance of Chinese gold medallist swimmer Ye Shiwen as "disturbing".

Ye shaved around five seconds off her personal best and swam faster in the last 50m than the winner of the men's event to break the world record and win gold in the 400m medley.

All medal-winners at the Olympics are automatically drug tested. There is no evidence of doping against Ye.

However, the executive director of the World Swimming Coaches Association, John Leonard, described her performance as "unbelievable".

Previous world record holder Stephanie Rice called it "insanely fast", while BBC Sport presenter Clare Balding asked: “How many questions will there be ... about somebody who can suddenly swim so much faster than she has ever swum before?”

Ye has denied the allegations of doping, insisting: "There is no problem with doping. The Chinese team has a firm policy so there is no problem with that."

However, Chinese swimmers failed 40 drug tests between 1990 and 2000, including World Championship winners.

Five more Chinese swimmers were banned for failing drugs tests in 2009 and in March this year 16-year-old Li Zhesi tested positive in an out-of-competition test.

Arne Ljungqvist, the International Olympics Committee medical commission chairman, said: “I have not personally any reason other than to applaud what has happened, until I have further facts. To suspect someone for having done something because he (or she) performed extraordinarily is a bit sad for Olympic sport.”

But Dr Ross Tucker, a doping expert at the Sports Science Institute of South Africa, wrote on his Science of Sport blog: “Does anyone who knows China's ethos and attitude towards Olympic sport actually believe that they would NOT deliberately dope their young athletes to win medals?”

Twitter was filled with posts from the Chinese public who are outraged by the doping claims.

"Don't suspect other people's success while you never saw how hard they fought for it," wrote one.

Triple jump world record holder Jonathan Edwards said on Twitter "I feel very uneasy about accusations being leveled at Ye Shiwen - she's 16! I'd prefer to believe in brilliance until proven otherwise" 

Image: Getty