Civilians maimed in devastating barrel bombings by Syria's regime in the divided city of Aleppo face a dire shortage of surgeons, wheelchairs and artificial limbs, a humanitarian group said Wednesday.

A chronic lack of medical equipment as well as inadequate post-operative care mean doctors often carry out amputations when normally the limb could be saved, Doctors Without Borders (MSF) said.

Finding a wheelchair is almost impossible, while prosthetic limbs and rehabilitation are in short supply, the group said in a report on the bleak situation in rebel-held areas of Syria's second city.

Some people bring blown-off limbs into hospitals with the wounded in the hope that they can be reattached, but a lack of facilities means this is usually impossible, MSF said.

Only about 100 doctors remain working in Aleppo's overwhelmed hospitals, compared with 2,500 across the city at the start of the conflict.

"The rest have fled, become internally displaced or refugees, or have been kidnapped or killed," the report said.

Regime forces began dropping barrel bombs on rebel-held eastern neighbourhoods of Aleppo in December 2013.

They are typically constructed from large oil drums, gas cylinders or water tanks filled with high explosives and scrap metal.

With international attention focused on the US-led military campaign against the Islamic State jihadist group, the regime has stepped up its use of the crude munitions in recent months.

"You could be sleeping. You could be walking to the shop. At any time a bomb can happen," said an MSF health worker quoted in the report.

After a barrel bombing, survivors often collect body parts, put them in bags and bury them according to Islamic principles, the report said.

President Bashar al-Assad has personally denied his forces use barrel bombs, saying the Syrian army has no indiscriminate weapons.

But MSF says barrel bombs have left thousands of civilians dead and wounded, among the more than 210,000 killed since the conflict began in March 2011.

Bombardments have knocked out most of Aleppo's infrastructure, including power lines.

Fearing attacks from the sky, aid organisations are often unable to deliver help to civilians in need.

"In Aleppo we now celebrate when it is a dark and cloudy day. Then we know we will have some hours of respite before the next bombings start," said one former resident who has fled to Turkey like thousands of others.