There could be as many as three million "undocumented" Zimbabwean citizens in South Africa, said Deputy Foreign Affairs Minister Aziz Pahad.
The Zimbabweans are in South Africa to escape their country's economic and political crisis, and there is little the government can do about it, Pahad said.
Pahad said this figure was separate from Zimbabwean professionals who have proper documents and were working in various sectors of South Africa's economy.
Pahad was answering questions from the media yesterday in Pretoria during a briefing on the government's international relations, peace and security cluster.
He said: "This figure is quite high and that's why for us the solution of Zimbabwe's political, social and economic issues is fundamental because we get affected."
South Africa and other African countries would defend Zimbabwean President Robert Mugabe's right to attend the European Union-African summit in Portugal from December 8 to 9, Pahad said.
"Our view has consistently been that nothing stops anybody from putting any topic on the agenda," he said.
"Africa will not move from its position that you cannot determine what constitutes the African delegation. There's a lot of fear.
"Today it's Zimbabwe, tomorrow it could be us and the next week it could be someone else.
"If we allowed that to happen, it would not allow us to have a unity of approach on how we deal with the Europeans on many fundamental issues," said Pahad.
He said he hoped the question of Mugabe attending the summit would be handled "sensitively".
Mugabe is banned from the EU.
Pahad said the government believed that Zimbabwe was in a state of crisis, with its 5000 percent inflation, the collapse of its currency and rising unemployment.
Donor countries have reportedly drawn up a rescue plan for Zimbabwe on condition that Mugabe step down.
President Thabo Mbeki was appointed in March by Southern African leaders to mediate talks between political groups in Zimbabwe.