The convoy, which was stationary at the time of the explosion, was moving pro-regime refugees near the war-torn city of Aleppo when the blast occurred.
Two buses were completely destroyed. Syrian sources reported seeing at least 100 bodies strewn everywhere.
The convoy was part of deal between the Syrian government and rebel factions that also include prisoner exchanges.
Efforts had been made to conceal the explosives inside the vehicle. Local sources said that the rigged car appeared to be packed with food supplies.
It is not immediately clear who the perpetrators of the attack are.