The lorry was on a level crossing when it was hit by the train at about 7am (05:00 GMT) on Monday, Minnie said.
A police spokesman told the SAPA news agency that the lorry driver suffered minor injuries.
"There don't seem to be any barriers at this level crossing," he said.
An official for the wine farm where the workers were employed on contract, said: "This is a terrible day. It is a great disaster. They were just innocently coming to work."
The crash is one of the worst in South Africa in recent years.
Nine people died and 59 were injured in April last year after a bus rammed into a freight train in the northern Limpopo province.