More people could die from disease than from bombings in the Gaza Strip if its health system is not repaired, a World Health Organization spokesperson said today.

Gaza health authorities deemed reliable by the United Nations say more than 15,000 people have been confirmed killed in Israel's bombardment of Gaza, around 40 percent of them children, with many more dead feared to be lost under rubble.

Israel has sworn to annihilate Hamas, the group that rules Gaza, after its gunmen burst across the fence and killed around 1,200 people and seized 240 captives on October 7, according to Israel.

"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," said the WHO's Margaret Harris at a UN briefing in Geneva.

She repeated concerns about a rise in outbreaks of infectious diseases, particularly diarrhoeal diseases.

Citing a UN report on the living conditions of displaced residents in northern Gaza, she said: "(There are) no medicines, no vaccination activities, no access to safe water and hygiene and no food. We saw a very high number of cases of diarrhoea among infants," she said.

She described the collapse of Al Shifa Hospital in northern Gaza as a "tragedy" and voiced concern about the detention of some of its medical staff by Israeli forces during a WHO evacuation convoy.

James Elder, a spokesperson from the UN Children's Agency in Gaza, told reporters by videolink that hospitals in Gaza were full of children with war wounds and gastroenteritis from drinking dirty water.

"I met a lot of parents... They know exactly what their children need. They don't have access to safe water and it's crippling them," he said.

He described seeing one child with part of his leg missing lying on the hospital floor for several hours, without receiving treatment for lack of medical staff.