Twelve people were injured when their taxi overturned on the N12 near the Putfontein off-ramp on the east of Johannesburg on Saturday, said emergency workers.
Netcare 911 spokesman, Chris Botha said it was unclear what led to the accident.
"Paramedics arrived at the scene and found the crumpled remains of the taxi obstructing the highway," he said.
"After triaging they found that one person had sustained critical injuries, the other eleven commuters sustained injuries ranging from serious to minor."
The critically injured patient was airlifted to the Charlotte Maxeke hospital while the others were transported by ambulance to a nearby hospital.