Syrian government forces Sunday made major advances in the divided city of Aleppo, threatening to drive a wedge through the rebel-held eastern sector, according to state media, a monitoring group and official sources.
Meanwhile, over 4,000 civilians fled into Kurdish-controlled areas and the Hanano district which fell to the government the previous day, according to the Syrian Observatory for Human Rights.
Local activists said many others were on the move inside the besieged eastern enclave, trying to get to areas less affected by government shelling and airstrikes.
It is the first time that large numbers of civilians have crossed to government-held areas since eastern Aleppo came under siege in July, despite intense airstrikes on the east and lack of food and healthcare.
Government ally Russia has announced the opening of safe corridors for civilians on several occasions and has accused rebels of preventing people from leaving the enclave.
The UN, however, has said that security issues and fear of arrest by government forces were deterring people from crossing the frontlines.
Government forces pressed into parts of the key rebel-held district of Sakhour after gaining full control of the neighbouring Hanano district the previous day, the Britain-based Observatory reported.
The advances, the most rapid by the government in months of fighting, mean that its forces are now only 500 metres from its existing positions in western Aleppo, the Observatory said. If they connected up, they would divide the rebel-held eastern sector in two.
Activists and locals painted a grim picture of the situation inside the enclave, which has been devastated by more than four years of government shelling and airstrikes.
"Anyone standing in one of the main streets of besieged Aleppo would be certain ... that Doomsday had come," activist Rami Zien wrote on Facebook.
"Tens of thousands of displaced people are walking, with no transport available. ... All the injured are being carried by foot to what remains of the destroyed emergency rooms," he wrote.
One civilian contacted by dpa said: "It's all over," and refused to comment further, while a rebel official commented bitterly about what the opposition sees as a lack of adequate outside support.
"Whoever has aircraft can win, and whoever has anti-aircraft weapons can resist, but those who permit aircraft to bomb cities while banning anti-aircraft weapons have decreed that [President Bashar] al-Assad will remain," Yasser al-Youssef, spokesman for the Nour al-Din al-Zenki rebel group, said.
Some 250,000 to 300,000 civilians are thought to be trapped in the enclave, which has been devastated by more than four years of government airstrikes and has been surrounded since July.
Food supplies in the area are running low and aid group Doctors without Borders says eight out of nine hospitals are no longer functioning after suffering repeated hits in airstrikes.
UN envoy Jan Egeland on Thursday said rebels had agreed to a humanitarian ceasefire to allow aid into the city but similar promises from the Syrian government and Russia were still outstanding.
Over 200 civilians, including 27 children, have been killed since the government launched its current offensive in Aleppo on November 15, according to the Observatory.
The government advances come as it makes strategic gains on the southern and western outskirts of Damascus, where it has effectively starved rebels out of areas they held through most of the five-year conflict.
Meanwhile, the UN children's agency UNICEF warned that nearly half a million Syrian children are living in besieged areas, a number it said has doubled in less than a year and includes some 100,000 children in eastern Aleppo.
"Children are being killed and injured, too afraid to go to school or even play, surviving with little food and hardly any medicine,” said Anthony Lake, UNICEF executive director.
UNICEF reported that in one besieged area, a group of volunteers built an underground playground and park by linking a series of basements where children could play without fear of bombs.
Most sieges in Syria are imposed by government forces, although Daesh also besieges government-held areas of the eastern city of Deir al-Zour and two Shiite villages in north-western Syria are besieged by rebels.
