The Syrian military has gained control of 98 percent of eastern Aleppo, with human rights observers saying the battle is over.

They say the rebels have withdrawn from the six remaining districts they’d held, and it “feels like doomsday” in the city.

“The battle in eastern Aleppo should end quickly. They (rebels) don’t have much time. They either have to surrender or die,” Lieutenant General Zaid al–Saleh, head of the government’s Aleppo security committee, told reporters in the recaptured Sheikh Saeed district.

Fighters of the Free Syrian Army fire an anti-aircraft weapon in the rebel-held Mashhad area in southeastern Aleppo, as the battle reaches its final phase. Photo: Stringer/AFP/Getty

Thousands of people have fled the siege barricades since the aerial attack intensified two weeks ago.

Approximately 10,000 people are thought to have gone to regime or Kurdish held territory in the last 24 hours, and the exact number of people left in the area is unknown.

Those who remain are believed to be packed into a small sliver of territory which is under siege.

Final message – I am very sad no one is helping us in this world, no one is evacuating me & my daughter. Goodbye.- Fatemah #Aleppo

— Bana Alabed (@AlabedBana) December 12, 2016

The rout of rebel forces has come much more quickly than most people expected.

Syrian President Bashar al-Assad, backed by Russia, is now close to taking back full control of Aleppo, which was Syria’s most populous city before the war and would be his greatest prize so far after nearly six years of conflict.

A Syrian rebel spokesman said opposition fighters are retreating in eastern Aleppo under intense government fire that is putting thousands of civilians at risk, calling the collapse “terrifying”.

https://twitter.com/bentaub91/status/808329752234917893

this is a call and might be the last call.
Save Aleppo people. Save my daughter and other children. #StandWithAleppo

— @Mr.Alhamdo (@Mr_Alhamdo) December 12, 2016

The military statement on the collapse of rebel forces came hours after Syrian forces, aided by Shiite militias from Lebanon, Iraq and Iran, took Sheik Saeed, one of the largest neighbourhoods in the southern part of the rebel territory, tightening the noose on the enclave.

The military also said its multi-pronged ground push on Monday captured the al-Fardous neighbourhood, one of the most populated districts to the north of Sheik Saeed.

Rami Abdurrahman, the head of the Britain-based Syrian Observatory for Human Rights, said the district remains under fire and that fighting continues there.

He estimated that about seven per cent of the enclave remains under rebel control.

“The situation is very, very critical,” said Ibrahim al-Haj, a member of the Syrian Civil Defence.

“The military took many areas and we are now squeezed.”

Smoke billows from the former rebel-held district of Bustan al-Qasr as Syrian government forces retake the embattled city. Photo: Stringer/AFP/Getty

Al-Haj had been on the move to find a place to keep him and his family away from the clashes and possible government capture.

Bassam Haj Mustafa, a senior member of the rebel Nour el-Din el-Zinki group who is in contact with fighters inside the city, said Monday the fighters are doing “their best to defend what is left”.

Tens of thousands of civilians have fled to government-held western Aleppo since the offensive began last month.

But tens of thousands remain trapped in the ever-shrinking eastern enclave.

Every message now that I'm receiving from east Aleppo is preceded with "this may be my last message". The heart breaks.

— Kareem Shaheen (@kshaheen) December 12, 2016

A rebel fighter from inside Aleppo, speaking on condition of anonymity for fear of reprisals, said the fall of Sheik Saeed means the fall of the enclave’s only mill and grains warehouse, which leaves the territory without access to bread or flour.

Meanwhile Pope Francis has appealed to Syrian President Bashar al-Assad in a personal letter to ensure that international humanitarian law is respected so that civilians are protected and aid can get to them, the Vatican says.

In the letter, given to Assad by the Vatican ambassador in Damascus, the Pope appealed to Assad and the international community for an end to violence and condemned “all forms of extremism and terrorism from whatever quarter they may come”.

– AAP with agencies