An explosion believed to have been caused by a car bomb tore through a Syrian border post near a refugee camp on the frontier with Turkey on Thursday, killing at least five people and wounding dozens more, the Syrian Observatory for Human Rights monitoring group said.

Ambulances transported the injured to the southern Turkish city of Kilis, where a state hospital official said at least 40 people were being treated.

A Turkish border official said the blast near Turkey's Oncupinar border post, which sits opposite the Syrian Bab al-Salameh gate, could be felt several kilometres away, but that the border gate remained open.

Abu Osama, a camp administrator, said the explosion happened behind his office and at least 20 tents were reduced to rubble.

Thousands of people have been fleeing the Syrian city of Aleppo, some 60km south of Kilis, in recent weeks because of a campaign of improvised "barrel bomb" attacks by President Bashar al-Assad's forces. 

"We have had thousands of new refugees come to this area the past 20 days because of the barrel bombing in Aleppo," Abu Osama said.

Turkey is sheltering more than 600,000 refugees from Syria's civil war and has kept its border open throughout the conflict.

Source: Reuters