Video report by ITV News reporter Sejal Karia
Syrian rebels including jihadists have begun a major counter-attack, detonating car bombs and launching more than 150 rockets from eastern Aleppo, the Syrian Observatory for Human Rights has said.
The British-based war monitor said 15 civilians had been killed and 100 wounded by rebel shelling of government-held western Aleppo.
State media reported that five civilians were killed.
Photographs showed insurgents approaching Aleppo in tanks, armoured vehicles, bulldozers, make-shift mine sweepers, pick-up trucks and on motorcycles, and showed a large column of smoke rising in the distance after an explosion.
Rebels said they had taken several positions from government forces, but a Syrian military source said the attack on the western side of the city had been thwarted.
A state television station reported that the army had destroyed four car bombs.
Aleppo has become the centre of the six-year conflict between President Bashar al-Assad backed by Iran, Russia and Shi'ite militias, and Sunni rebels including groups supported by Turkey, Gulf monarchies and the United States.
Abu Anas al-Shami, a member of the Fateh al-Sham media office, told Reuters from Syria the group had carried out two "martyrdom operations", after which its fighters had gone in and had been able to "liberate a number of important areas".
A third such attack had been carried out by another Islamist group. A senior official in the Levant Front, a Free Syrian Army (FSA) group, said: "There is a general call-up for anyone who can bear arms."
He added: "The preparatory shelling started this morning."