The World Health Organization said that already around 160 children are killed every day in Gaza, and the UN children's agency UNICEF warned that the number could skyrocket.
Hamas attacked Israel on October 7, killing around 1,200 people, mainly civilians, and taking around 240 people hostage, according to Israeli officials.
Israel's relentless bombing campaign and ground offensive has killed more than 13,300 Palestinians, including at least 5,600 children, according to the territory's Hamas-run health ministry.
"If children's access to water and sanitation in Gaza continue to be restricted and insufficient, we will see a tragic — yet entirely avoidable — surge in the number of children dying," spokesman James Elder said.
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More than 1.7 million of Gaza's 2.4 million inhabitants are estimated to be internally displaced within the enclave -- nearly half of them children, the UN said Tuesday.
Nearly 900,000 of those displaced are staying in severely overcrowded shelters run by UNRWA, the UN agency that supports Palestinian refugees.
On average, there are 700 people to one shower unit and 150 people to a toilet in those shelters, Elder said.
The WHO said last week that only 10 of the territory's 36 hospitals were still functioning, with the situation deteriorating since then. It said Monday there are no functioning hospitals in northern Gaza.
WHO said it had been asked by health personnel to help evacuate three non-functioning hospitals in the north: Al-Shifa and Al-Ahli in Gaza City and the Indonesian hospital near the Jabalia refugee camp.
WHO warned that Gaza's health system was struggling to cope amid an influx of casualties and sharp increases in diseases.
More than 72,000 cases of upper respiratory infections had been detected in displacement shelters, Lindmeier said.
There had also been nearly 49,000 cases of diarrhoea among children under five -- 31 times the monthly average.
Cases of scabies, lice, chicken pox and skin rashes are also surging.
UNICEF said no cholera had yet been detected in Gaza, but stressed that an outbreak could see the number of children dying in Gaza rise "exponentially".
Agencies