Motorists had to run for cover on the N12 freeway in Westonaria on Thursday afternoon when more than 20 armed robbers blocked a money van with a truck, Krugersdorp police said.
Constable Audrey Sefara said more than five cars were caught in the middle of the robbery when the group of men blocked the freeway with a truck and assaulted the cash van driver and his crew.
Sefara said it was not clear what led to the robbers fleeing empty-handed and abandoning a silver Toyota Hilux at the scene.
The men got away in a navy blue Toyota Corolla and a black Yaris. None of the passing motorists were hurt.
Netcare 911 spokesman Nick Dollman said eye witnesses said the gang used automatic rifles to attack the cash van.
He said paramedics attended to a cash-in-transit guard who was assaulted and had sustained a contusion near his right eye. - Sapa