The International Organization for Migration (IOM) said it was preparing for a "possible exodus of vulnerable Zimbabwean migrants fleeing threats of post World Cup xenophobic violence in South Africa."
South African security forces moved into townships in the Cape Town area on Monday after attacks and threats against foreign migrants workers. Scores of workers took refuge at police stations after shops run by migrants were looted.
The IOM had no figures for Zimbabweans crossing at the border town of Beitbridge in the past week, but said they had seen unusually high numbers of trucks laden with furniture and household goods, indicating people were leaving homes and jobs.
"People have clearly stated that they are returning indefinitely because of the fear of violence," IOM spokesman Jared Bloch told a news briefing in Geneva.
More than 90 percent of 140 Zimbabwean migrants interviewed by the IOM at the weekend upon return to their homeland said that they had fled threats of violence. The other 10 percent said they had already suffered xenophobic violence.
The World Cup ended on Sunday.
South Africa has attracted millions of workers from across the continent who compete with locals for scarce jobs and resources. Two years ago more than 60 people were killed during anti-foreigner attacks.
"These are not idle threats people are responding to. They have a very real memory of what could happen," Bloch said.
An estimated 1.5 million to 2 million Zimbabweans work and live in South Africa, according to the Geneva-based IOM.
Its contingency plans include pre-positioning food and hygiene packs on the Zimbabwean side of the border and measures to speed processing of documents in case of a large influx.
