Lausanne - The World Anti-doping Agency (WADA) said on Wednesday it had filed an appeal against a decision to clear Chinese swimming star Sun Yang of missing an out of competition doping test.

WADA, meeting in Lausanne, told AFP that it had filed the appeal with the Court of Arbitration for Sport (CAS) following a decision by swimming's world governing body FINA not to pursue a case against the multiple world champion.

Sun, who has won Olympic gold in the 200m, 400m and 1 500m freestyle, missed an out-of-competition test on September 4 at his home in China's Zhejiang province.

"WADA has filed a CAS appeal in the case of Sun Yang," a spokesperson for the anti-doping authority said.

The swimmer - who was banned for three months in 2014 for taking a stimulant - was cleared of wrongdoing by FINA in January, according to his lawyers.

Sun failed to comply with the test requirements but a FINA doping panel cleared him of wrongdoing because testers for IDTM - the body which conducts tests - had breached several rules.

Those included failing to produce authorisation letters and a nursing licence, his lawyers said in a statement.

Sun's lawyers also threatened legal action against a British newspaper, the Sunday Times, which claimed Sun clashed with the anti-doping testers and he and a bodyguard smashed a sealed vial of blood with a hammer.

Sun is one of China's greatest-ever athletes and is hugely popular at home. But his career has been dogged by controversy over doping suspicions and he was publicly branded a drug cheat by his Australian rival Mack Horton at the Rio Olympics in 2016.