Syria and Russia have announced four more humanitarian corridors into the rebel-controlled city of Aleppo.

Dozens of families made their way out of the rebel-controlled areas of the city. The Syrian government holds the western part of the city, while eastern Aleppo is still under the dominion of rebels.

"Since the start of the humanitarian operation ... 169 civilians have left the neighbourhoods controlled by illegal armed groups through the exit points," Russian defense ministry said in a statement.

"As the UN, and as humanitarians, we welcome any initiative aimed at assisting civilian populations in warzones, particularly in Syria today. We are, in principle and in practice, in favor of humanitarian corridors, under the right circumstances, that allow the protection of civilians," Staffan de Mistura, the UN Special Envoy for Syria, told journalists in Geneva.

"As for the current situation on the ground ... Aleppo city is now almost completely encircled by Syrian troops ... There needs to be guarantees on the protection of civilians, whether they choose to remain in Eastern Aleppo, or move to other areas of their choice, as offered through the corridors," he added.

The governments of Syria and Russia said that the corridors will permit distribution of food and medical aid to civilians. The countries will also give rebels an option to surrender and leave the city through the corridors, CNN reported.

Russia said that 69 rebels had surrendered and over 50 people were given medical treatment after the opening of humanitarian corridors.

The city of Aleppo is continually under siege and aerial bombardment, and many hospitals were also struck. Reports say the city has severe shortages of food, water, medicine, and fuel.

"I am deeply alarmed by the disturbing developments in and around Aleppo city. Hundreds of mortars, missiles and projectiles were launched on both eastern and western Aleppo in past weeks, resulting in scores of deaths and hundreds of injuries," said Stephen O'Brien, UN Emergency Relief Coordinator.

O'Brien expressed his concern about airstrikes in the city: "Strikes, by all sides, continue to be launched on and from heavily populated areas from air and ground without regard for civilian presence. Attacks on other civilian infrastructure remain an almost daily occurrence in some areas."

UN had proposed a 48 hour pause in the air bombardment so that humanitarian supplies could be delivered to the civilians.

"How do you expect convoys of humanitarian aid to actually reach those people if there is shelling and bombing from the air and from the ground?" said de Mistura.

About 250,000 people remain in Aleppo after about four years of intense battle between Syrian government and rebels.

The UN had earlier said that the city was at the brink of starvation, as it had not received supplies in weeks before the humanitarian corridors were opened.