The BBC's Milton Nkosi says it is believed the taxi was carrying 20 passengers when it went over a bridge and hit a train as it plunged onto a railway line below.
South Africa has an exceptionally high accident rate on its roads.
At least 10,000 people die on the roads a year, mostly due to reckless driving.
No-one on the train was injured, according to ENCA news.
A minibus taxi has collided with a train near Ballito in South Africa, killing at least 14 people, according to KwaZulu-Natal emergency services.