The Western Cape Department of Mobility has urged motorists to use alternative roads, following a fire incident in the Huguenot Tunnel, in the early hours of Saturday morning.
The South African National Roads Agency said the tunnel might be closed for about two weeks.
A bus exploded and lit up the tunnel.
Authorities are now assessing the damage and investigation are underway.
Alternative routes are via the N1 Wolsley -Wellington-Paarl, Paarl-Wolsley-Worcester, the N2 is accessible via Worcester and Villiersdorp, light motor vehicles can also use the Bainskloof Pass, as well as the R101 Du Toitskloof Pass.
Heavy vehicles are cautioned against using the R46 and the Theronskloof Pass.