Residents said warplanes began bombing the city in the latter half of Sunday.
"The bombing started again," a Syrian White Helmet rescue worker named Ismail Abdullah told CNN by phone from eastern Aleppo.
"I heard a lot of bombing in the night. They were airstrikes."
Civilians urged to evacuate
The Syrian government and its close ally Russia announced the start of the ceasefire last Tuesday.
Originally, it was only expected to last eight hours, but ended up stretching several days.