An Israeli missile struck a building inside the compound housing Gaza's largest hospital on Monday, medics and an AFP correspondent said.
The attack hit a building close to the main gate of Shifa hospital in Gaza City, medics said.
An AFP correspondent at the scene said a wall of a building inside the compound was damaged by a missile apparently fired by a drone.
There was no immediate comment from the Israeli army.
Statistics published by OCHA, the UN humanitarian agency, show that some 22 hospitals, clinics and medical centres have been hit and damaged by Israeli shelling since the devastating military operation began on July 8.
In a statement issued shortly before the strike, the World Health Organisation said it was "appalled" by the number of strikes on healthcare facilities and personnel.
"The World Health Organisation has been appalled by the continuing trend for healthcare facilities, staff and vehicles to come under direct fire in Gaza since the escalation of violence on 8 July 2014," a statement from the Geneva-based body said.
"It is vital for health facilities and staff to be able to perform their life-saving work without fear of attack," it said, recalling that all parties are obliged under international humanitarian law "to "protect medical services."