The explosion occurred at a roadblock manned by hardline Islamist fighters at the entrance of the rebel-held crossing, several hundred yards from the Turkish side, activists said.
The wounded were rushed to Turkish hospitals. Dogan reported seven people killed but the Turkish foreign ministry said it had no information yet.
Pictures taken by activists at the scene showed several burnt and mangled cars and an engine block that apparently flew to the side of the road from the vehicle.
“The casualties are all civilians, from the people queuing to cross,” activist Omar Aref said.
No specific group was blamed for the attack. Suspects will include forces loyal to Assad, although tensions have been rising between hardline Islamist groups linked to Al-Qaeda and more moderate rebel forces, leading to sporadic clashes and killings.
The explosion in Bab Al-Hawa took place a day after Turkish forces shot down a Syrian helicopter that had entered Turkey’s airspace. The Syrian army accused the Turkish government, which backs the uprising against Assad, of trying to escalate tensions along the border.
More than 100,000 people have been killed since the uprising against Assad broke out in March 2011. Violence has often spilled over into neighboring Turkey and Lebanon, and sometimes into Jordan and Israel.
Syria’s state news channel said government forces seized control of Shabaa, a suburb next to the Damascus airport road, on Tuesday. Rebels denied the reports and said the battle was still going on.
Rebels near the capital say that Assad’s forces appear to be emboldened after the United States backed away from threats to take military action against Assad’s forces in response to a chemical weapons strike on opposition-held Damascus suburbs that killed hundreds of people.
Over the weekend, Washington and Moscow agreed a deal to remove chemical weapons from Syria but government air strikes resumed.
Video from Lebanon’s news channel Al Manar showed soldiers touring empty tunnels in Shabaa dug by rebels, who used them to transport men and arms while under air and artillery strikes.
Rebels in Damascus say they are regrouping and making new plans now that a foreign strike appears unlikely.
“The fighters are having ‘operations rooms’ meetings to try and plan new battles. They will be launched from several points,” said a fighter from the Islam Brigade in Damascus.
“It will be a big new offensive but this will still need some time,” he said.