Police have closed the M7 road to allow emergency services to work following a 15-vehicle pile-up involving three trucks and one motorbike on Friday morning.
Garrith Jamieson, an advanced life paramedic, said they had initially been responding to a truck and car collision on the Bellville Road offramp Durban bound.
While emergency services was attending to the initial accident, Jamieson said another collision occurred just behind them in the backlog involving two trucks, 10 cars and a motorbike.
Jamieson said more emergency services were dispatched to attend the 12 people who were injured.
He said the 12 people suffered moderate injuries and were taken to hospital.
Rain is expected throughout the day and motorists are advised to exercise caution on the road as there are many parts in the city that are waterlogged.