The study, commissioned by the Uasa trade union, said projects linked to South Africa's hosting of the 2010 Soccer World Cup would provide incentives for new illegals.

"It's definitely a staggering number and more are bound to cross the borders, attracted by the prospects of 2010 and beyond," said economist Mike Schussler of financial services group T-Sec, who wrote the report.

"An average South African is six times better off than an average Zimbabwean and twenty times better off than an Malawian, so that draws people," he told a news conference.

But Schussler said the widespread view in South Africa that illegal immigrants took jobs away from locals was overstated, with research indicating that one in five immigrants created their own job in a boost for the national economy.

Increasing xenophobia

"Yes, some of them are involved in criminal activities.

"But South Africa has attracted skilled immigrants as well - some start their own informal businesses and are not as much of a burden to the social system as believed."

South Africa's unemployment rate, estimated by some economists as high as 40%, is a political issue for the ruling African National Congress and analysts say the country is growing increasingly xenophobic as more foreigners arrive.

South Africa deported nearly 210 000 illegal aliens last year, mostly to neighbouring Zimbabwe which is in the grip of an economic meltdown and political crisis, the research found.

Economists believe as many as 3.5 million Zimbabweans have sought to leave the country, with most headed for South Africa but others going to Britain or the United States.

'SA has become like the US'

Uasa officials said the government needed to address the Zimbabwean situation urgently to reverse the influx of immigrants - something President Thabo Mbeki's government has been reluctant to do so far.

"At present, fewer than 1.2 million Zimbabweans are (formally) employed in their country. There are more Zimbabweans employed in South Africa than in Zimbabwe," said Koos Bezuidenhout, chief executive of Uasa.

Zimbabwe's economy has been shrinking for six consecutive years with inflation reaching a world record of 1 070% and jobless rate of 80%.

But Schussler said the positives of having so many illegal immigrants far outweighed the negatives for South Africa.

"America was built by immigrants, and South Africa has become like the United States of Africa," said Schussler, adding that immigrants often had the very skills that South Africa was losing as its own skilled emigrants head for Australia, Europe or the United States.