The UN Relief Agency for Palestinian Refugees (UNRWA) said wheat, flour and other supplies had been pillaged at several warehouses.

"This is a worrying sign that civil order is starting to break down after three weeks of war and a tight siege," said UNRWA's Gaza chief Thomas White.

One of the warehouses in the central town of Deir al-Balah had been used to store supplies from humanitarian convoys that began crossing into Gaza from Egypt on October 21, it said.

"Thousands of people broke into several UNRWA warehouses and distribution centres in the middle and southern areas of the Gaza Strip, taking wheat flour and other basic survival items like hygiene supplies," UNRWA said.

Israel has been bombarding the Gaza Strip since October 7, the Palestinian health ministry says has killed more than 8,000 people, half of them children.

It also imposed a total blockade on normal food, water, medicine and fuel deliveries into Gaza, with the first convoy of humanitarian aid entering only two weeks later.

Since then, UNRWA says 84 aid trucks have crossed into Gaza but aid agencies say the numbers are far too low. Before the war, UN figures showed an average of 500 trucks a day entering Gaza.

"Supplies on the market are running out while the humanitarian aid coming into the Gaza Strip on trucks from Egypt is insufficient," said White.

"The needs of the communities are immense, if only for basic survival, while the aid we receive is meagre and inconsistent," said the UN official.