The explosion was caused by "a fault in the storage of oxygen cylinders", the medical sources said, adding that several dozen people had also been wounded.

Videos on social media showed firefighters trying to extinguish flames at Ibn al-Khatib hospital on the southeastern outskirts of the Iraqi capital as patients and their relatives tried to flee the building.

A medical source at the hospital told AFP "30 patients were in the intensive care unit" reserved for the most severe cases of Covid-19 in Baghdad.

The civil defense told Iraqi state news they "rescued 90 people out of 120 patients and their relatives" at the scene, but would not give the exact number of dead and wounded.

The fire, which according to several sources was caused by negligence, often linked to endemic corruption in Iraq, immediately sparked a heated reaction on social media in the country.

Baghdad Governor Mohammed Jaber called on "the health ministry to establish a commission of enquiry so that those who did not do their jobs may be brought to justice".

In the middle of the night, while the civil defense said the fire was under control, the health ministry had not issued any statement or announced how many people had been killed or wounded.

On Wednesday, the number of Covid-19 cases surpassed one million in Iraq, which has recorded the highest number of infections in the Arab world.

The health ministry has recorded a total of 1,025,288 cases of the disease and 15,217 deaths since the first infections were reported in the country in February 2020.

The ministry has said it carries out around 40,000 tests daily from a population of 40 million.

Iraq's hospitals have been worn down by decades of conflict and poor investment, with shortages in medicines and hospital beds.

Those patients who can often prefer to source oxygen tanks for treatment at home, rather than go to overcrowded and run-down hospitals.

The country launched its vaccination campaign last month, and has received nearly 650,000 doses of different vaccines -- the majority by donation or through the Covax programme, which is supporting lower and middle income nations to procure vaccines.

As of Wednesday, 274,343 people had received at least one dose, the ministry said.

Health authorities have faced an uphill battle to convince Iraqis to get vaccinated, in the face of widespread scepticism over the jab and public reluctance to wear masks since the start of the pandemic.