A Syrian monitoring group and rescue workers in opposition-held areas in Syria say a series of airstrikes has hit a hospital and nearby buildings, killing at least 20 people in the northern city of Aleppo.

The victims include three of the hospital's medical staff.

The head of the Britain-based Syrian Observatory for Human Rights says the airstrikes took place shortly before midnight on Wednesday and that at least one child was among the 20 killed.

The Syrian Civil Defense, volunteer first-responders in rebel-held areas, gave a higher toll, saying the strikes on the Quds hospital killed 22. The dead included one of the few remaining pediatricians in opposition-held areas of the contested city. The Syrian Civil Defense said there were four consecutive airstrikes against the hospital and adjacent buildings.