ALEPPO, Syria — The disfigured bodies of women and children brought into Aleppo's largest hospital bear witness to the intensity of the fighting in residential districts of Syria's second city.

"The majority of casualties are caused by buildings crashing down on civilians," said Abu Abdu, who works as a general surgeon in Al-Shifaa.

The hospital mortuary received the corpses of four people on Tuesday, including the crumpled remains of a woman and a young boy, crushed to death when their homes collapsed over their heads.

Another 17 people were wounded in aerial attacks, including a young girl, who was reportedly hit by a shower of shrapnel that fell on her kindergarten. The hospital also treated a rebel who took a sniper bullet to the stomach.

Hospital records show that in the 48 hours to Monday, Al-Shifaa's doctors treated 69 wounded civilians and registered 15 deaths.

One doctor said the full civilian casualty toll in Aleppo was much larger, as the hospital's records did not include the figures from smaller clinics or field hospitals around the city.

"The tolls that appear on TV are not reflective of reality -- the casualties in Aleppo are far higher," said Doctor Abu Ismail.

He estimated a daily average of 25 civilians killed and 100 wounded since the city became a major battleground between troops and rebels on July 20.

Hospital volunteer Um Suheib said: "We have every kind of casualty from every kind of weapon. We want our children and civilians to be safe. Let the armies square off and leave us alone."

Instead troops and rebels are locked in urban combat in the cobblestone lanes of the Old City, with the front lines in perpetual flux as checkpoints and sniper positions shift daily.

The commander of the rebel Al-Khattab Brigade said that the fighting in the Old City had claimed the lives of four of his men in the past three days, most of them killed by snipers.

He said forces loyal to President Bashar al-Assad had suffered "heavy losses" but gave no figure.

"Most of the casualties are civilians because they are hitting residential areas," the commander added, declining to give his name.

Doctors said that bakeries in the city had been hit "at least seven times" this month alone, leading to a high civilian toll as residents were forced to venture out to queue for bread.

The latest hit on a bakery on Sunday left 11 people critically wounded, the medics said.

More than 15 loud explosions were heard in the city in the space of just 60 minutes on Tuesday.

The fighting focused on the Maysaloon neighbourhood, on the fringes of the Old City, and in Bab al-Nayrab on the road to a military airport of the same name.

In the southwest of the city, where the army launched a major offensive earlier this month to recapture rebel-held neighbourhoods, the battle lines were also fluid.

The carcasses of burnt out buses sealed off streets under rebel control, while stones and tyres marked off roads leading into areas held by Assad's forces.

The army recaptured the Salaheddin neighbourhood but the adjacent Saif al-Dawla district remains in the hands of the rebels.

In the city centre, smoke rose over Aleppo's historic UNESCO-listed Citadel, as, in the cool shade of one of the Old City's historic market inns, rebels cleaned and loaded ageing Kalashnikovs.

"There are clashes in this city every single second," said rebel fighter Abu Alaa. "You just never know when they will erupt."