As an unrelenting Israeli bombardment intensified on Saturday, bakeries in Gaza were running out of bread, drinking water was in short supply and power outages left families without charged phones to find out if fleeing relatives were safe.

"There is an electricity crisis, food crisis, water crisis, a crisis of everything," Eyad Abu Mutlaq, 45, said in Khan Younis in south Gaza, a region filling up with thousands of people fleeing the north for fear of an Israeli invasion.

"It is only God who can resolve it," he said after touring four bakeries to find long queues or no supplies.

The flood of people arriving in south Gaza after Israel told them on Friday to leave an area in the north has stretched resources that were already strained to breaking point.

The UN has urged Israel to "avert a humanitarian catastrophe" in Gaza, a slither of land with 2.3 million people wedged between Israel, Egypt and the Mediterranean Sea.

In its response to the devastating October 7 assault from Gaza by Palestinian militant group Hamas, Israel has imposed a "total blockade" halting food supplies and cutting electricity to Gaza. A week after that began, shops were running out of many items.

"I was looking for basic food, eggs, rice, canned food, even milk for the children and I couldn’t find them," said Khan Younis resident, giving only her nickname of Um Salem. "This is how Israel is fighting us, through starvation of our children. They either kill children by bombs or soon by starvation."

Israel said it had told people to leave the north for their safety and to ensure they were not caught up in the conflict. It said it would guarantee the safety of Palestinians fleeing the area on two main roads until 4pm (1300 GMT) on Friday.

Those who have fled say many roads and streets are often difficult to use, and some impassable, because of damage.