Loud hailers are also being used to announce the unilateral ceasefire backed by Russia.
Syrian state media says the army has opened exit corridors from the besieged east, with buses standing ready to evacuate civilians and fighters.
Reuters says Russia has told the UN it will stop bombing eastern Aleppo for 11 hours a day for four days.
Initial reports suggest however that few are taking up the opportunity to leave.
Armed groups say the goal of Moscow and President Assad’s forces is to empty the area of civilians, so that they can move in to take over.
Intensified Russian and Syrian bombing of besieged rebel-held parts of Aleppo in the past weeks has hit hospitals, bakeries and water pumping stations, and killed hundreds of civilians.
Russian state media reports claim Islamist rebels have shot at civilians trying to flee during the truce, leaving several people injured.
The United Nations has criticised unilateral ceasefires after long sieges, saying they can be helpful only if combined with humanitarian access for those who do not want to leave.
Since Russia intervened in the war a year ago, the government’s side has gained the upper hand on numerous fronts, including Aleppo, where the opposition-held sector has been completely encircled for weeks.
The rebels, however, say they are preparing a large-scale offensive to break the siege of Aleppo and that the Russian air force has failed.
“The coming battle is not going to be like others. We are waiting for the signal of the start of a decisive battle which will surprise the regime and its militias,” Abu Obeida al Ansari, a commander from Jabhat Fateh al-Sham, the rebranded former al Qaeda affiliate Nusra Front, said in a statement on social media. (Euronews)