Distressing messages and reports are emerging from those trapped inside the city.
In video testimony aired on the BBC, Syrian civilians describe the uncertainty and the fear in the last remaining rebel-held areas of Aleppo.
"Oh my god. All the people were happy and excited about the agreement and evacuating the city finally, and they were just preparing themselves. They think the regime has a ground force ..."
"Good morning my friends. Tens of shells are reigning down on the besieged area of Aleppo. There are injured in the field hospitals, injured as a result of the bombardment by the regime forces and allied Iranian militias."
The evacuation of tens of thousands of civilians was supposed to begin on Wednesday.
But a ceasefire deal between rebels and the Syrian government collapsed, and fighter jets resumed deadly air raids.
For the last year, UK-based Channel Four News has been broadcasting the work of 25 year-old Waad al-Kateab, a young woman who has filmed life in rebel-held East Aleppo.
Her work as a film-maker has seen her win two Amnesty International awards but now, like many others, she's unable to leave.
Ms al-Kateab sent this audio message to Channel Four.
"There is heavy shelling around the hospital, it's mortars and air forces are flying so I don't know if it's okay. I don't want to go out from the city. It's my Aleppo, it's my lovely city. Maybe it's just some place in our hearts to be strong. Maybe this disaster will be finished and we will be okay."
Channel 4 News Editor Ben De Pear says he is very concerned for her welfare, and for all those without adequate resources.
"We were hopeful that she would follow some of the injured who were going to go out last night, injured people put on buses, they got to the frontline, the ceasefire fell apart and they've come back today. And the hospital is now filled with not only the injured who've been in there for the past few months, but the freshly injured because the onslaught has started again. So we're very worried about her, we're worried about the doctors she's with - there are 110 medical staff there are 300 or 400 injured people and there are up to 500 children."
Mark Seawright is the executive director at Relief Aid, a humanitarian organisation working inside eastern Aleppo.
He's told the ABC 40 members of his team are trapped and are reporting continued fighting around the area.
He says there are concerns about a lack of food, water and medical care.
"They are continuing to report significant fears of detention by government forces and are also continuing to have to shelter in buildings with large numbers of people. Four to five families in a house, with little shelter, no food, people down to one meal a day and no access to safe drinking water let alone medical care. So it's a dire situation, I think we've been talking about crisis but now we talk about catastrophe."
The United Nations says renewed bombardment of civilians hoping to be evacuated has almost certainly violated international law.
Activist Linda Shamy uploaded this video to Twitter calling for continued activism to ensure safe passage for civilians.
"Please do not stop, do not stop to post, to tweet, to speak, to shout. Now after Iranian militia have revoked the ceasefire. We need you more. You already did a great job by moving the negotiations into a positive level. We need you now to the streets. Do no surrender, do not stop until the last person is evacuated safely from the besieged city. God bless you all."
