Heavy rains have flooded tens of thousands of tents where displaced residents have been living in Gaza, with a United Nations official saying almost everyone in the territory needs help.
Residents used pots and pans to clear water from their flooded tents, with some saying they were left without shelter.
Jonathan Veitch, the Unicef representative for Palestine, said the "desperate" situation was being made worse by Israeli restrictions on the entry of heavy machinery and supplies such as engine oil.
Some 90% of Gaza residents have been displaced by the Israeli war against Hamas, many of them multiple times, with limited access to clean water and sanitation.
Aid agencies say the situation is likely to worsen with the start of the rainy season.
Speaking to the BBC from Deir Al Balah in central Gaza, Veitch said: "It's just horrific and they're absolutely desperate.
"We're providing all the assistance that we can but we're getting stopped on the street as we're driving now because people are begging us for help."
The Hamas-run government in Gaza said about 70,000 tents had been flooded. A spokesperson said the "collapse of dozens of cracked walls and roofs" had caused injuries, some of which were critical.
Veitch also said there were fewer tarpaulins, plastic sheeting and tents available in the Gaza strip due to UN budget cuts.
"We have to be much more choosy about where we're going to be supporting," he said.
"But unfortunately, heavy flooding this morning means that nearly everyone needs help."
Veitch said aid workers were being "stopped on the street" by Gazans "begging us for help".
He continued: "They're absolutely desperate. We saw last year what winter does, and we had deaths from hypothermia last year.
"We can expect the same again unless we have very, very urgent action now."
A ceasefire came into force in Gaza in October last year, but Israeli air strikes have continued almost every day.
Since then, 1,580 people have been killed, according to Gaza's Hamas-run health ministry, whose figures are considered reliable by the UN. Israel says it is targeting Hamas, but often civilians are also killed.
Meanwhile, a peace plan for Gaza, brokered by the Trump administration, has stalled.
The ceasefire saw thousands of Palestinians held by Israel released in return for all of the 48 remaining hostages held in Gaza, and an agreement to end the war.
The conflict was triggered by the Hamas-led attack on Israel on 7 October 2023, when about 1,200 people were killed and 251 taken hostage.
Since the war began, 74,594 people have been killed in Gaza, according to the territory's health ministry.
