The N3 northbound was closed near to Frankfort and Reitz in the Free State on Friday morning, due to a fire that broke out when a truck collided with another vehicle.
The N3 Toll Concession (N3TC) said the accident happened between the Frankfort/Vrede and Roadside/Reitz interchanges.
"All northbound lanes [toward Gauteng] are closed. Northbound traffic is being accommodated via contra-flow on the southbound carriageway.
"Traffic congestion and heavy delays can be expected in this area. Road users are requested to slow down and approach the area with caution," N3TC spokesperson Anita Heyl said.
Another truck crash and fire occurred on the N3 on Thursday, near to the Heidelberg Traffic Control Centre. It led the closure of the northbound lanes in the vicinity.