Women and children were among the dead in the blast in an area used as a car park, the UK-based Syrian Observatory for Human Rights said.
The area around the crossing has been targeted by car bombs before, AFP reported.
In February, a blast on the Syrian side killed six people and wounded 45.
The Syrian side of the crossing is under the control of Islamic Front which has been battling the Islamic State of Iraq and the Levant since early January.
Other border crossings between Turkey and Syria have also been targeted, including the Bab al-Hawa post in Idlib province in the northwest, where two suicide bombers killed 16 people in January.