Cluster bombs have left entire streets in flames after the Syrian government announced a major offensive on rebel-held areas.
Sky sources said at least five different parts of Aleppo had been targeted on Thursday evening, as a week-long truce collapsed.
Video footage showed buildings on fire and a journalist for the AFP news agency said his street in the Bustan al-Qasr district was burning.
The destruction in the contested city’s rebel-held eastern quarters was caused by a combination of air strikes and shelling.
In a statement carried on state news the government forces called on citizens to keep away from “terrorist groups”.
It said it would provide shelter to any residents leaving the neighbourhoods through designated safe passages.
The 250,000 residents of east Aleppo, which rebels have held since 2012, have been living under government siege since early September.
Activists say at least 12 people were killed in presumed government or Russian airstrikes and shelling on the eastern quarters on Thursday.
President Bashar al Assad has denied bombing civilians in Aleppo and has blamed the West for much of the destruction.
The announcement of new strikes came as the US and Russia convened a last-ditch meeting in New York to save their ceasefire plan.
After the meeting of the International Syria Support Group, US Secretary of State John Kerry said the ceasefire was not revived.
France demanded Syria ground its planes, while the Netherlands said the new Syrian government offensive sent the wrong signal.
Russia, meanwhile, said “nothing happened”.