A 25-year-old Australian standing trial on charges of trying to smuggle methamphetamine has told a court he came to China to buy a muscle-building supplement and didn't check the package he purchased before trying to depart.

Peter Gardner, who also has dual New Zealand citizenship, was detained in the southern city of Guangzhou on November 8 when police said he was trying to smuggle more than 30 kilograms of methamphetamine out of China.

Gardner could face the death penalty if convicted.

He told the court he didn't knowingly smuggle drugs, though he also acknowledged wrongdoing and offered to remedy the situation by helping police identify what he referred to as Chinese suspects.