Video of a small boy, bloodied and covered in dust, who was rescued after an apparent air strike in the Syrian city of Aleppo, sparked outrage and concern on social media on Thursday.

Sitting alone in an ambulance, the boy — identified by doctors as five-year-old Omran Daqneesh — looked dazed and shocked, staring silently as he tried to wipe the blood off his head, seemingly unaware of his injuries.

Twitter user Charlene Deveraturda @malasadasbooks posted an image of the boy and wrote: "Poor baby. Near my grandson's age. I cannot imagine. The image does not leave my mind. #syrianboy #Syria #peace."

The hashtag #Syrianboy was one of the top trending topics in the United States and Britain.

More than 10 tweets were posted every minute on Twitter with the hashtag, according to social media analytics company Zoomph. Many linked images of the child with a picture of Aylan Kurdi, a Syrian boy whose body was found on a beach in Turkey last year.

The video of Omran and other children being pulled from the rubble caused widespread upset and condemnation over the harrowing reality of Syria's five-year-old civil war.

Twitter user Malcolmite (@Malcolmite) wrote: "It's not important if it goes viral, what's important is what is going to be done about it? #syrianboy." Sara Assaf (@SaraAssaf) tweeted: "So if this terrorized little boy turns into a terrorist one day ... Who is to blame? #SyrianBoy #Aleppo #Injustice."

Aleppo, split into rebel- and government-controlled areas, has become the focus of the fighting in Syria.

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

'The real face' of Syria's war

"That little boy has never had a day in his life where there hasn't been war, death, destruction, poverty in his own country," US State Department spokesman John Kirby told reporters during his daily press briefing.

"You don't have to be a dad, but I am. You can't but help look at that and see that that's the real face of what's going on in Syria," Kirby said.

The American roadmap to end the war includes a national ceasefire, opening up of humanitarian aid, and the resumption of political negotiations between the Syrian regime and opposition in Geneva.

Under a cessation of hostilities, Kirby said, people would hopefully be spared "any more images like the one of that young boy today in Aleppo".

The video, shot on Wednesday in the rebel-held al-Qaterji neighbourhood, shows an aid worker carrying the little boy out of a building and seating him inside the ambulance, before rushing back to the scene of the bombing. 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 from 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, Aylan Kurdi, who washed up on a Turkish tourist beach.

The image of Aylan, who died when a smugglers' boat taking his family and other refugees to a nearby Greek island capsized, swept across social media and was retweeted thousands of times.