The accident occurred on Tuesday around 10 kilometres outside the town of Bambari, around 300 km northeast of the capital Bangui, as the truck was travelling to a weekly market day in the village of Maloum.
"At the moment, we have counted 78 dead and 72 wounded. Some wounded were taken directly to their homes from the accident scene and died there some time after, but most died here," said Chamberlain Bama, chief doctor at the university hospital in Bambari, according to Reuters news agency.
A member of parliament from Bambari said the truck was overloaded and travelling faster than normal.
"They were driving fast to make it to the market on time. That's what probably caused the accident," Amaseka Topi told Reuters.
Most of the people killed were travelling on the back of the lorry, local trader Oumar Tidjani told the DPA news agency.
Decades of neglect have left the landlocked country's road system in ruins and safety regulations are rarely enforced.
Due to lack of other transportation, people in the Central African Republic regularly resort to travelling in overloaded trucks, which are often in a poor condition.