The accident happened on Thursday morning, spokesman Kwanele Ncalane said in a statement.
He said the truck was trying to avoid an oncoming vehicle when it lost control and hit the bakkie.
At least two people were seriously injured and three others sustained minor injuries. They were taken to a nearby hospital, he said.
Those who died were occupants of the bakkie.
Transport MEC Willies Mchunu urged drivers to be vigilant on the road.
“I am deeply saddened by the loss of lives in such a gruesome manner. I reiterate our call for all road users to remain vigilant and patient as well as adhere to road traffic rules.”
With the Easter season approaching, more officials would be present on the roads.
“I would like to send my deepest condolences to the families of the deceased and wish those in hospital a speedy recovery,” Mchunu said.