"I don't know what is going to happen to us," said 38-year-old Mohamed Rukby, an unemployed father-of-four in the Bustan al-Qasr neighbourhood.
"We have nowhere to go. All the roads are closed and we've been suffering for days with shortages of bread, food and basically everything," he told AFP.
Food and fuel shortages had already hit the east of the city, home to around 300,000 people, after government forces advanced to within firing range of the key Castello Road supply route on July 7.
But over the weekend, regime forces seized the road itself, completely severing the eastern rebel-held portion of Aleppo city from the outside world and raising fears of a potentially devastating siege.
"I'm scared of what comes next," said Rukby.
"Maybe the regime will not be content with besieging us and will attack the eastern neighbourhoods."
In the opposition-controlled Al-Mashhad district of the city, mechanic Mohamed Zeitun said his work had dried up because a shortage of fuel meant residents were not driving anywhere.
"The idea of the siege keeps me up at night," the 44-year-old told AFP.
"I don't have supplies to last me more than a week, and if there is no food in the markets, there could be a famine," the father-of-five said.
Aleppo city was once Syria's economic powerhouse, but it has been ravaged by the war that began in March 2011 with anti-government protests.
The conflict has killed more than 280,000 people and left Aleppo divided roughly between government control in the west and rebel control in the east.
Analysts said the advance by the government, which has been backed by a major Russian air offensive, was a significant blow for rebels in Aleppo.
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"Besides the humanitarian catastrophe under way, recent events in eastern Aleppo are politically very significant," said Karim Bitar, an analyst at the Paris-based Institute of International and Strategic Relations.
"It has now become mission impossible for Syria's rebels who are completely deprived of any breathing space," he added.
The advance also leaves Syria's President Bashar al-Assad feeling "considerably more secure than a few months ago," he said, meaning his forces could move "to further consolidate his positions."
'Aid urgently needed'
The encircling of eastern Aleppo has raised international concern, with the UN's humanitarian coordination body OCHA warning that "the situation is particularly worrying due to the high concentration of people living in this area."
It said eastern Aleppo had not received humanitarian supplies since July 7, and that there was enough food there to last 145,000 people for one month.
OCHA said some essentials had been stockpiled and there were sufficient emergency medical supplies for four to five months.
But "further life-saving aid is needed urgently," it added.
"Safe, unimpeded and sustained humanitarian access into east Aleppo city is critical to save lives and reduce suffering," the body said in a statement, adding it had begun advocacy on the possibility of cross-line aid deliveries.
About 600,000 Syrians already live under siege throughout the country, according to the UN.
Most are living under sieges imposed by government forces, though rebels and the Islamic State group have also used the tactic.
In some places, civilians have reportedly starved to death or died for lack of medical supplies because of siege tactics.
Despite successive rounds of talks, international efforts to find a solution to the conflict have yet to bear fruit, and UN Syria envoy Staffan de Mistura has urged Russia and the United States to push for renewed peace talks in Geneva next month.
But the opposition High Negotiations Committee said the regime's advance around Aleppo could jeopardise new talks.
"This is pushing the negotiations in Geneva to a more remote date. Frankly the prospects are becoming less and less possible or more and more remote," HNC member Basma Kodmani said on Sunday night.