Three partially functioning hospitals treating severely wounded patients and sheltering thousands of displaced Palestinian civilians in northern Gaza are now out of service after coming under intense Israeli fire, a Gaza health official told Al Jazeera.

Israeli forces bombed al-Awda Hospital in Jabalia early on Saturday, and have also shelled Kamal Adwan and the Indonesian hospitals in Beit Lahiya over the past few hours.

“We cannot count the number of those killed. The numbers are terrifying,” the official told Al Jazeera.

At least one person has been killed and several others were wounded in the strike at the entrance of the laboratory of Kamal Adwan Hospital, Gaza’s Health Ministry said.

The Palestinian news agency Wafa also reported that because of the military siege, two intensive care unit patients at the Indonesian Hospital died on Saturday.

On Friday, health officials appealed for fuel, medical supplies and food to be sent immediately to the three northern Gaza hospitals which have been overwhelmed by the number of patients and injuries.

The World Health Organization (WHO) has also accused Israel of preventing at least 50 medical specialists belonging to eight groups from entering Gaza, the first such case of entire organisations being blocked from participating in humanitarian efforts in the besieged territory.

Northern Gaza, once home to more than half of the territory’s 2.3 million people, was bombed to rubble in the first phase of Israel’s assault a year ago.