Six people were killed when a truck and car collided on the N4 toll road towards Mbombela near Montrose on Sunday afternoon.
Mpumalanga Department of Community Safety and Security spokesperson Moeti Mmusi said the deceased included three adults and three children, all occupants of a Mercedes-Benz.
"They all died at the scene on impact," Mmusi added.
He said the critically injured driver of the sedan was airlifted to a nearby hospital in Mbombela.
Three pedestrians were slightly injured after being hit by debris.
Mmusi said a stationary Toyota Tazz on the side of the road was also slightly damaged.
"The cause of the collision has not yet been established, but the investigation is already under way."
In a separate accident on Sunday, five people were killed on the R544 between Verena and Emalahleni.
"Motorists are therefore advised to be cautious to avoid further loss of lives on the road," Mmusi said.