"There are 50 casualties and they are being transported to Bab al-Hawa (crossing) and to another hospital in Atmeh," witness Abdallah Saleh told Reuters on Sunday.

Others said that at least nine people were killed in the terrorist attack.

Reuters also reported that the field hospital was damaged in the blast.

It was not immediately clear who was responsible for the attack, but Atmeh lies in land held by foreign-backed militants seeking to overthrow the Syrian government. Atmeh, which is part of the Idlib Governorate, is also home to a growing refugee camp.

According to initial reports from Reuters, the hospital is owned by Ghassan Aboud, a Persian Gulf-based Syrian businessman who runs a private television channel and charitable foundations for helping refugees.

Sunday's car bomb attack comes three days after more than a dozen people were killed when a car bomb tore through a Syrian refugee camp at a border post on the frontier with Turkey.

At least 14 people were killed after the explosion at the Bab al-Salameh crossing on Thursday, The Daily Star reported.

Syria has been gripped by deadly violence since 2011. Over 130,000 people have reportedly been killed and millions displaced due to the unrest.

NTJ/HH