An Australian court has ordered the retrial of two alleged drug traffickers because the judge in their original court case repeatedly fell asleep.

"Periods of sleep became longer as the trial went on. Members of the jury were visibly detracted and, at times, amused," the High Court court said.

Rafael Cesan and Ruben Mas Rivadavia were convicted in 2004 of importing ecstasy and jailed for over a decade each.

In their appeal, the judge in the original 17-day trial was described as sleeping at intervals of up to 20 minutes, with periodic snoring.

"A substantial miscarriage of justice resulted," the court said, ordering a fresh trial.

Medical evidence showed the judge had been suffering from severe obstructive sleep apnoea.