Initial reports said five people died in the blast, while nine others were injured.
According to an Anadolu Agency correspondent on the ground, a bomb planted in a diesel fuel tanker was detonated in the Tirende area, south of the Afrin district center.
The fuel spreading around triggered a fire after the explosion.
The Observatory and the medical sources said many other people had been injured in the explosion, some very badly.
In early 2018, Turkey conducted Operation Olive Branch to remove the PKK terror group's Syrian affiliate the People's Protection Units (YPG) from Afrin. The Turkish military and the Free Syrian Army (FSA) entered Afrin town center and liberated it from terrorists on March 18.
Following the operation, Turkey has been involved in efforts to rebuild the town's infrastructure, as well as health and education institutions.