China's triple Olympic swimming gold medallist Sun Yang has been found guilty of refusing to give a doping sample and banned for eight years in a ruling that excludes him from the Tokyo Olympics and effectively ends his career.

The judgement from the Court of Arbitration for Sport (CAS) upheld the appeal by the World Anti-Doping Agency (WADA) against swimming's ruling body (FINA) and Sun, 28, who had already served a three-month doping ban in 2014.

Sun, idolised in China, was accused of refusing to provide blood and urine samples when drug testers visited his home in China in September 2018, vowed to appeal the ruling, while WADA hailed the ban as a "significant result".

"This is unfair. I firmly believe in my innocence," Sun told China's Xinhua news agency. "I will definitely appeal to let more people know the truth."

Any appeal would be at the Swiss federal court. A vial of Sun's own blood sample was smashed with a hammer during the testing session in 2018, but the swimmer was acquitted by FINA of anti-doping violations, agreeing that testers had failed to produce adequate identification.

But the ruling outraged WADA which took the matter to CAS, demanding a ban of between two and eight years for missing the out-of-competition test. CAS said its panel had "unanimously determined" that Sun had tampered with his doping control. Taking into consideration his previous doping ban, CAS said it had imposed the stiffest eight-year sanction, meaning he will miss this summer's Tokyo Olympics.