The Court of Arbitration for Sport (CAS) earlier accepted an appeal from the World Anti-Doping Agency (WADA) against a decision by swimming body FINA to clear Sun of wrongdoing for his conduct during the 2018 test.

CAS said the eight-year ban was imposed because Sun already had an earlier anti-doping rule violation against him from 2014.

"This is unfair. I firmly believe in my innocence," he told Xinhua. "I will definitely appeal to let more people know the truth."

Sun and members of the 28-year-old's entourage had smashed vials containing blood samples taken at an out-of-competition test in September 2018.

The Chinese is reigning world and Olympic champion in 200m freestyle and won two gold medals at the 2012 London Games and another at Rio de Janeiro in 2016 but is also a controversial figure in the sport.

At the Rio Games, Australian rival Mack Horton accused him of being a "drug cheat".

At last year's Gwangju world championships in South Korea, 400m freestyle silver medallist Horton refused to share a podium with Sun, who won the gold while competing under the shadow of the appeal.

The gesture drew applause from other swimmers but a warning from FINA.

The case has attracted huge interest in China, where Sun is currently training at the Zhejiang College of Sports in Hangzhou, and the swimming world.

A FINA report said Sun questioned the credentials of the testers before members of his entourage smashed the vials with a hammer.

Sun had argued during the CAS hearing, which was heard in public, that the testers failed to prove their identity and behaved in an unprofessional manner.

"The CAS Panel unanimously determined, to its comfortable satisfaction, that the athlete violated Article 2.5 FINA DC (Tampering with any part of Doping Control)," the CAS statement said.

"In particular, the Panel found that the personnel in charge of the doping control complied with all applicable requirements as set out in the ISTI (International Standard for Testing and Investigation).

"More specifically, the athlete failed to establish that he had a compelling justification to destroy his sample collection containers and forego the doping control when, in his opinion, the collection protocol was not in compliance with the ISTI."

The statement added that it was "one thing, having provided a blood sample, to question the accreditation of the testing personnel while keeping the intact samples in the possession of the testing authorities.

"It is quite another thing, after lengthy exchanges and warnings as to the consequences, to act in such a way that results in destroying the sample containers, thereby eliminating any chance of testing the sample at a later stage."

WADA welcomed the ruling as "a significant result" in a separate statement and said it was "satisfied that justice in this case has been rendered."

Tens of thousands of Chinese flooded social media in support of Sun Yang following the verdict, stating it was "cruel" and "unjust".

"Foreigners are jealous. It is really unfair to treat Sun Yang in this way. Since when did competitive sports become villain sports," said one user called 'Lingering memories' on microblogging website Weibo Corp.

Australian Associated Press