Thousands of people have been evacuated from the last rebel bastion in Aleppo is under way as part of a ceasefire deal that may end years of fighting for the city and mark a major victory for Syrian President Bashar al-Assad.

A first convoy of ambulances and buses with nearly 1,000 people aboard drove out of the devastated rebel-held area of Aleppo, which was besieged and bombarded for months by Syrian government forces, a Reuters reporter on the scene said.

Syrian state television reported later that two further convoys of 15 buses each had also left east Aleppo. The second had reached the rebel-held area of al-Rashideen, an insurgent said.

The International Committee of the Red Cross has said some 3,000 civilians and more than 40 wounded people, including children, had already been evacuated.

Women cried out in celebration as the buses passed through a government-held area, and some waved the Syrian flag.

Mr Assad said in a video statement the taking of Aleppo was a historic moment.

An elderly woman, who had gathered with others in a government area to watch the convoy removing the rebels, raised her hands to the sky, saying: "God save us from this crisis, and from the (militants). They brought us only destruction."

Wissam Zarqa, an English teacher in the rebel zone, said most people were happy to be leaving safely.

However he added: "Some of them are angry they are leaving their city. I saw some of them crying. This is almost my feeling in a way."

Earlier, ambulances trying to evacuate people came under fire from fighters loyal to the Syrian government, who injured three people, a rescue service spokesman said.

"Thousands of people are in need of evacuation, but the first and most urgent thing is wounded, sick and children, including orphans," said Jan Egeland, the UN humanitarian adviser for Syria.

Behind those fleeing was a wasteland of flattened buildings, concrete rubble and bullet-pocked walls, where tens of thousands had lived until recent days under intense bombardment even after medical and rescue services had collapsed.

Timeline of offensive to retake Syria's Aleppo

Turkey is considering establishing a camp in Syria for civilians being evacuated from Aleppo and the number of people brought out of the city could reach 100,000, Deputy Prime Minister Veysi Kaynak said.

In Aleppo's rebel-held area, columns of black smoke could be seen as residents hoping to depart burned personal belongings they do not want to leave for government forces to loot.

A senior Russian general, Viktor Poznikhir, said the Syrian army had almost finished its operations in Aleppo.

However, the war will still be far from over, with insurgents retaining their rural stronghold of Idlib province to the southwest of Aleppo, and the jihadist Islamic State group holding swathes of the east and recapturing the city of Palmyra this week.

The International Committee of the Red Cross said close to 1,000 civilians and 26 wounded, including several children, were evacuated, a total it expects to double by day's end.

The ICRC said there was "very light screening" by Syrian authorities without identity checks and registrations.

Rebels and their families would be taken towards Idlib, a city in northwestern Syria which is outside government control, the Russian defence ministry said.

Idlib province, mostly controlled by hardline Islamist groups, is not a popular destination for fighters and civilians from east Aleppo, where nationalist rebel groups predominated.

A senior European diplomat said last week that the fighters had a choice between surviving for a few weeks in Idlib or dying in Aleppo.

"For the Russians it's simple. Place them all in Idlib and then they have all their rotten eggs in one basket."

Idlib is already a target for Syrian and Russian air strikes but it is unclear if the government will push for a ground assault or simply seek to contain rebels there for now.

The International Rescue Committee said: "Escaping Aleppo doesn't mean escaping the war ... After witnessing the ferocity of attacks on civilians in Aleppo, we are very concerned that the sieges and barrel bombs will follow the thousands who arrive in Idlib."

Britain's Foreign Secretary Boris Johnson said he had summoned the ambassadors of Russia and Iran to convey profound disquiet over Aleppo, saying it was crucial to protect civilians and deliver aid.

UN chief Stephen O'Brien will brief the Security Council tomorrow on the Aleppo evacuation.

Devastation in Aleppo