Untreated diseases could eventually kill more people in Gaza than bombings if the health system is not restored, the World Health Organization (WHO) says.
Diarrhoea and respiratory infections are widespread among children in overcrowded UN facilities where almost 1.1 million people are sheltering.
Patients with chronic illnesses like cancer are also not receiving treatment.
WHO spokeswoman Dr. Margaret Harris told a news conference in Geneva that an assessment of those shelters had found outbreaks of infectious diseases, with cases of diarrhoea among children aged five and older more than 100 times normal levels by early November.
No treatment is available for them, she said, without which infants in particular can deteriorate and die very quickly.
According to the UN, only five hospitals are partially operational in the north of Gaza, the area that has been the focus of the Israeli ground offensive.
Eight of the 11 hospitals are functional in the south, where the Israeli military has ordered civilians to flee. Only one of those hospitals has the capacity to treat critical trauma cases or perform complex surgery.
“Eventually, we will see more people dying from disease than we are even seeing from the bombardment if we are not able to put back [together] this health system,” Dr. Harris warned.
Addressing journalists via video link from Gaza, on Tuesday, Unicef spokesman James Elder reported seeing hospitals full of children with horrendous war wounds.
He described seeing one child missing part of his leg lying untreated on a hospital floor for several hours because of a lack of medical staff. Other injured children were lying in car parks and gardens outside, he said.
However, the UN noted that they are calling again for a permanent ceasefire.