"Early this morning we saw a helicopter and a spotter plane fly overhead. Ten minutes later, there was heavy shelling," said Walid al-Fares, an activist living in Khalidiya, one of the neighbourhoods where mortars bombs have landed.
Another resident said that government loyalists were using heavy machine guns to shoot into the area.
Rami Abdelrahman, head of the British-based Syrian Observatory for Human Rights, said shells were being fired at a rate of one a minute.
Abdelrahman said there had also been overnight clashes in rural Aleppo.
"People said they heard explosions and shooting after rebels attacked a police station and then clashed with police," he said.