A Chinese anti-doping official on Monday warned the country's athletes to avoid "accidental mistakes" during their stay in London.

Three thousand tests had been planned for the athletes who were expected to make it to London at the beginning of the year and the program will draw to a close by the end of July as all 396 athletes leave for London.

China Anti-Doping Agency's deputy head Zhao Jian was "confident" of sending a clean team to the Games with a strict doping-control program which helped catch Rome swimming world champion Li Zhesi of cheating in March.

"Generally speaking, the situation is good. After all these years of hard work in conducting doping tests and education, we think athletes are well aware of the risk of cheating," said Zhao. "I am confident that we can keep our 'zero' record in London."

China has been free from doping scandals at the Olympics since Atlanta 1996.

But Zhao admitted his worries that some athletes might "make mistakes".

"They know they must not use banned drugs but that's not enough to avoid positive tests. They also need to guard against accidental mistakes," Zhao said.

"They should report their whereabouts and therapeutic use exemptions, and use safe nutrition. I am a little worried that some of them just don't care about these things."

"I want to tell them: once you are found positive, you will be punished, no matter you violate the regulation wittingly or unwittingly," he added.

Zhao also revealed that the newly-adopted biological passport had been used this year.

"It has been used for three months so I can't tell you too much about the program. But I believe it will help a lot in doping control," he said.