His face bloodied and completely covered in dust, the little boy sits quietly, staring ahead, dazed and shocked after an apparent air strike in the Syrian city of Aleppo.

Alone in an ambulance, the boy - identified by doctors as five-year-old Omran Daqneesh - tries to wipe the blood off his head, unaware of the injury he has sustained.

Video of children being pulled from the rubble of a building hit by air strikes in Aleppo has been widely circulated on social media, causing upset and condemnation over the harrowing reality of Syria's five-year war.

Aleppo, split into rebel- and government-controlled areas, has become the focus of fighting in Syria's five-year conflict.

Rebel-held areas are suffering heavy air strikes daily as pro-government forces try to retake territory lost to rebels two weeks ago in the southwest of Aleppo.

The video was shot on Wednesday in the rebel-held al-Qaterji neighborhood of the city.

It shows an aid worker carrying the little boy out of a building and placing him on a seat inside an ambulance, before rushing back out to the bombed-out scene. The boy sits alone, stunned, before two more children are brought into the vehicle. A man with blood on his face then joins them.

Aleppo-based freelance photographer Mohammed Raslan Abu Sheikh, who was at the scene, said civilian rescuers and aid workers were elated as Omran was pulled out of the rubble alive with the rest of his family of six.

"He was in a state of shock, not even crying, he made us cry while he himself was silent, just watching us," Abu Sheikh told Reuters.

Last year, international sympathy for victims of Syria's war was heightened by a photo of a drowned 3-year-old refugee from Syria, Alan Kurdi, washed up on a Turkish tourist beach. The image of Aylan, who died when a people smugglers' boat taking his family and other refugees to a nearby Greek island capsized, swept across social media and was retweeted thousands of times.