South Africa Rugby said it could have sold its local ticket allocation for next year's Tests against the British & Irish Lions three times over, such was the demand.
The governing body held an online ballot for local fans to register their interest for tickets, which will be allocated on Friday, with 323,964 applications received for the tour.
Supporters from outside South Africa had a separate ballot, but no figures have so far been released on the number of applications received.
"As we expected, interest in the three Tests was extremely high – they are two to three times oversubscribed – but we are confident that we'll get as many people as possible into the stadiums," SA Rugby chief executive Jurie Roux said.
"We also know that not everyone will take up the tickets they are issued and there will be a resale phase later on, so all doors are not necessarily closed.
"But we do want to warn fans and discourage them from buying from illicit vendors as those tickets cannot be guaranteed."
The Lions are scheduled to play two Tests in Johannesburg and one in Cape Town on an eight-match tour from 3 July to 7 August next year.