An AFP journalist saw multiple bodies beside a damaged ambulance outside Gaza City's Al-Shifa hospital, which is overcrowded with civilians seeking shelter from Israeli bombing as well as those wounded.
Ghebreyesus said he was "utterly shocked by reports of attacks on ambulances evacuating patients close to Al-Shifa hospital in Gaza, leading to deaths, injuries and damage".
"We reiterate: patients, health workers, facilities and ambulances must be protected at all times. Always," the WHO chief wrote on X, formerly Twitter.
The Hamas government said Israeli forces hit "a convoy of ambulances which was transporting the wounded" from Gaza City towards Rafah in the south of the territory.
In the aftermath of the strike, the AFP journalist saw a child being carried away and a dead horse tied to a cart beside a blood-splattered Palestinian Red Crescent ambulance.
The Israeli military said it had launched an air strike on "an ambulance that was identified by forces as being used by a Hamas terrorist cell in close proximity to their position in the battle zone".
"A number of Hamas terrorist operatives were killed in the strike," a military statement said.
Gaza's health ministry announced "several citizens were killed and dozens wounded in an Israeli strike at the entrance to Al-Shifa hospital".
Lynn Hastings, the United Nations humanitarian coordinator for the Palestinian territories, expressed "alarm" over the strike "as patients were being evacuated to find safety".
Shifa has a bed occupancy rate of 164 percent according to the WHO, which on Wednesday warned a shortage of fuel for generators "immediately risks the lives" of patients.
Some 16 hospitals across Gaza are no longer functioning because of damage from strikes and the lack of fuel, the health ministry said.
More than 23,500 people have been wounded across Gaza in four weeks of war, the health ministry said, while the death toll has surpassed 9,200.
Around 1,400 people were killed in attacks by Hamas militants in Israel on October 7, sparking the war.
