Three people who are accused of making fake marriage documents to help foreign nationals become South African citizens have been arrested, police say.
When officers raided a building in Durban on Monday they seized application forms, copies of IDs and other evidence - which they said one of the suspects was caught trying to destroy.
Police believe many of the IDs were stolen from local women without their knowledge, then used to create fraudulent marriage certificates and visas for foreigners.
"When they come, they come as a married man to a South African woman. When they are here, they will divorce that woman," regional police spokesman Col Robert Netshiunda told news site News24.
"By that time, they got citizenship, so they brought more people.
"That's the scam they were [allegedly] running."
It is not clear how many people were involved in the alleged scheme or which countries the alleged payees came from.
Police say they are analysing computers and hard drives from the scene for more evidence.
The alleged office is housed in an unassuming building on a suburban road.
It was operating as a "clandestine home affairs office", Col Robert Netshiunda told national broadcaster SABC.
"They were facilitating marriages, visas and other services that Home Affairs would provide to South Africans."
The sophisticated operation may have involved an insider at the government department for Home Affairs, according to police, who say they have identified but not arrested a potential suspect.
South Africa boasts the continent's biggest economy, attracting jobseekers and migrants from the wider region, as well as smaller numbers from Europe and Asia.
In recent years there have been anti-immigration protests and waves of violence targeted at immigrants.
It became a campaign issue for May's general election, and the Patriotic Alliance (PA) that is now part of South Africa's coalition government was among political groups accused of stoking xenophobia.
BBC