Police spokeswoman Mary Martins-Engelbrecht said on Tuesday police were looking at whether the six heists were linked, and said the wave of attacks on Monday may indicate a new trend of gang hits on cash-in-transit vans.

"We are looking at the possibility of a link," Martins-Engelbrecht told SAFM radio. "A new trend may be rearing its ugly head."

Police have made four arrests, she said. No one was killed in the attacks on private security vans carrying cash in Johannesburg, Durban and other towns and cities in Africa's richest country. Local media said shots were fired and one security guard was injured.

South Africa, which has one of the world's highest rates of violent crime, last week pledged to stamp out organised crime after a series of violent attacks raised security fears ahead of the 2010 soccer World Cup, which South Africa will host.

A spate of violent robberies and bloody shootouts has shocked even the crime-weary country, prompting concerns that unbridled violence may mar the showpiece tournament.

Safety and Security Minister Charles Nquakula, who sparked outrage recently by saying people who complained about crime should leave the country, said last week police would focus on organised crime syndicates carrying out attacks on banks, shopping malls and vehicles carrying cash.