By Aidan Lewis and Emma Farge

(Reuters) -A breakdown of civil order has put four U.N. aid distribution centres and a storage facility out of action in Gaza as people search desperately for food and water, a U.N. Palestinian refugee agency (UNRWA) official said on Monday.

Tom White, director of UNWRA Affairs in Gaza, also said that a logistics base at the Rafah border crossing vital to aid distribution had become increasingly difficult to operate because 8,000 people were sheltering at it.

"With the breakdown of civil order, every day now we've got hundreds of people trying to get into the warehouses to steal flour," he told Reuters.

"Right now people are in survival mode. It's about getting enough flour and it's about getting enough water."

Thousands of Gaza residents broke into U.N. warehouses on Sunday to seize flour and other items. One of the warehouses, in Deir al-Balah in central Gaza, is where UNRWA stores supplies delivered by humanitarian convoys crossing into Gaza from Egypt.

"Effectively, we have lost Deir al-Balah. We'll see whether we can get that up and operational again, but of course it's complicated because right now the Rafah log (logistics) base has become a magnet for people who are either seeking shelter, seeking protection under the U.N. flag, or are trying to get into the warehouses to get flour," White said.

Aid to Gaza has been choked since Israel began bombarding the Palestinian enclave in response to an attack by the Hamas militant group on Oct. 7 that killed 1,400 people.

There has been a mounting international outcry over the toll from the bombing. Medical authorities in Hamas-run Gaza, which has a population of 2.3 million people, said on Monday that 8,306 people - including 3,457 minors - had been killed.

Rick Brennan, regional emergencies director of the World Health Organization, told Reuters WHO had not been able to resupply two hospitals in north Gaza, Al Shifa and Al Quds, because the U.N. had deemed the level of risk unacceptable.

“It's a disaster on top of a disaster. Health needs are soaring and our ability to meet those needs is rapidly declining," he said, adding a ceasefire was needed to enable a larger humanitarian operation.

A third of hospitals are non-functioning and 71% of clinics are non-functioning, he said. WHO is continuing to resupply hospitals and clinics in south Gaza, but relief delivered so far overall in Gaza is a "drop in the ocean" of needs, he said.

The Palestinian Red Crescent said so far 140 trucks of aid had entered Gaza since Oct. 7 and the biggest delivery so far of 33 trucks arrived on Sunday.

But U.N. officials say at least 100 trucks a day are required to cover Gaza's urgent needs. Before the war several hundred trucks were normally arriving in Gaza daily.

Aid entering from Egypt is being driven on a round trip of more than 84 km (52 miles) from Rafah for inspection on the Egypt-Israel border, triggering Egyptian complaints.

Israel says it does not want aid to enter from its territory or to fall into the hands of Hamas, refusing delivery of fuel, water supplies and relief distribution in Gaza.

On Sunday U.S. President Joe Biden and Egypt's Abdel Fattah al-Sisi committed to a significant acceleration of assistance. Several dozen trucks set off from the Egyptian side of Rafah on Monday, humanitarian and security sources said.

COLLAPSE OF SERVICES

But White said that due to delays, the situation was so bad that more aid could no longer be a solution, and a humanitarian ceasefire was needed. He added: "If the public sector collapses here, you're into a different magnitude of need."

UNRWA was unable to distribute flour to bakers on Sunday and was down to distributing one litre of potable water per person to displaced people, he said, adding that in a humanitarian response a survival rate was three litres per day.

White said Gaza's south had been overwhelmed by an influx of displaced people from the north. Access on roads was reasonable in the south but increasingly hard in the north due to damage and security as Israel attacked Gaza's main northern city.

Tommaso Della Longa, spokesperson of the International Federation of Red Cross and Red Crescent Societies, said Gaza was in desperate condition.

"The longer it continues the more we will see desperation," he said. "If you are not able to get supplies to people who are starving, people will find a way."

(Reporting by Aidan Lewis and Emma Farge; Additional reporting by Yusri Mohamed and Ahmed Mohamed Hassan in Cairo; Editing by William Maclean, Angus MacSwan and Jonathan Oatis)