Outbound motorists on Thika Road have been advised to use alternative routes following traffic build-up at Muthaiga.
It follows an accident that involved a passenger bus and a 14-seater matatu Tuesday evening.
The bus overturned and blocked a section of the road.
St John Ambulance sent out an alert advising motorists to avoid the route.
"There is a huge traffic snarl-up on Murang'a road/Thika road into and out of Nairobi CBD following an accident where a bus overturned at Muthaiga area. Police and rescue teams are on site. Avoid the route if you can."
Details on what caused the accident were yet to be relayed by authorities by press time.
