A 27-year-old man has been arrested at the OR Tambo International Airport after being in possession of a bag containing R6.9m, police said on Saturday.
The money, which was in US dollars and South African rands, was seized at the airport on Friday, said police spokesperson Brigadier Vish Naidoo.
He said the suspect was prevented from departing to Mauritius after his arrest.
"During a continuing and successful implementation of an integrated plan at the OR Tambo airport, the team, acting on intelligence, intercepted luggage suspected of containing undeclared cash," he said.
Naidoo said the suspect was arrested after police verified that the bag contained more than $199 000 and more than R4m.
He said the SAPS, the South African Revenue Services (SARS), the hawks and port security continued to work tirelessly to ensure that crime, including the smuggling of illicit contraband and undeclared cargo, was not committed at the country's ports of entry.
Naidoo added that the suspect was likely to face a charge of contravening the Customs and Excise Act.
He was expected to appear in the Johannesburg Commercial Crimes Court on Monday.