The regime gains have prompted an exodus of thousands of desperate civilians, some fleeing to districts held by the government or Kurdish forces, others heading south into areas still under opposition control.
"The situation is disastrous," said Ibrahim Abu Al-Leith, a spokesman for the White Helmets rescue group in the Ansari neighbourhood.
"There is mass displacement and morale is in the gutter," he said, his voice cracking with emotion.
"People are sleeping in the streets. They don't have anything to eat or drink, but neither do we," he told AFP.
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The opposition has steadily lost territory since Russia intervened to bolster President Bashar al-Assad in September 2015.
Yesterday, government forces seized the Sakhur, Haydariya and Sheikh Khodr districts, and Kurdish fighters took the Sheikh Fares neighbourhood from rebels, the Syrian Observatory for Human Rights monitor said.
"This is their (the rebels') worst defeat since they seized half the city in 2012," Observatory director Rami Abdel Rahman said.
The advances left all of northeast Aleppo under government control.
Syria's White Helmets warned on Monday they had no more fuel reserves for rescue vehicles.
Nearly 10,000 civilians have fled the east, the Observatory said late Sunday, with about 6,000 moving to the Kurdish-held Sheikh Maqsud neighbourhood and 4,000 to government-held west Aleppo.
Kurdish officials published a video they said showed civilians crossing a field to Sheikh Maqsud, where local forces helped people cross a makeshift barrier.
Syria's Kurds are officially aligned with neither the government nor the rebels, but the opposition views them as effectively allied with the regime in its efforts to recapture Aleppo.
People in southern neighbourhoods were donating blankets and other items to the new arrivals, who had travelled on foot, exhausted, cold and hungry.