A civil defence official, speaking on state television, said there had previously been deadly accidents at the same spot.
Khaled Ayadi, who had arrived at the scene after the accident, told AFP he saw the bodies of "people scattered (all around) and blood".
He said that he and other motorists who had stopped by the side of the road started to help and try to retrieve the bodies until the rescuers arrived and took over the gruesome task.
"On this road there are always accidents, especially [involving] trucks... We must find a solution for this road so there are no more accidents," Ayadi said, adding that Sunday's accident was overwhelming.
Social network users bemoaned the tragedy.
"What a heavy toll," one of them said.
Another denounced the "roads of death" in Tunisia and wrote: "24 dead and no one from the government has declared a national catastrophe".
The World Health Organisation in 2015 said Tunisia had the second worst traffic death rate per capita in North Africa, behind only war-torn Libya.
Experts blamed run-down roads, reckless driving and poor vehicle maintenance for a rise in accidents the following year.
Tunisian President Kais Saied and Prime Minister Youssef Chahed visited the scene of Sunday's accident, one of Tunisia's worst.
In April, seven women day labourers were among 12 people killed when the pickup truck taking them to work collided with a minivan in the impoverished central region of Sidi Bouzid.
In August 2016, at least 16 people were killed and 85 others wounded in another road accident in the mountainous region of Kasserine.
The authorities recognise the scale of the problem but have said the country's security challenges, including jihadist attacks, have kept them from giving it more attention.