The explosives-laden vehicle detonated near the Bab al-Salam crossing into Turkey, in northern Aleppo province, Syria. It was in a garage used by people crossing the border, said Rami Abdul Rahman, head of the London-based Syrian Observatory for Human Rights.
He added it was not clear if the incident was a suicide bombing.
Turkish government official Suleyman Tapsiz said initial reports indicated the jihadist Islamic State in Iraq and the Levant, known as ISIS, was responsible for the blast.
The area around Bab al-Salam was the site of an explosion in February which killed six people and injured 45 others. It is the primary route for Syrians fleeing to Turkey.