The International Committee of the Red Cross says more than 28,000 people in Gaza are staying at temporary shelters to escape fighting near their homes.
The Red Cross says Monday hundreds of families have fled their homes in the neighborhoods of Jabaliya, Beit Lahiya, and Zaytun in northern Gaza, as well as border areas in the south.
The statement said during the daily three-hour lull in fighting, residents struggle to find food and other supplies in nearly-empty stores. It also said most of the high-voltage lines bringing electricity from Israel into Gaza have been damaged, forcing hospitals to use generators for power.
The United Nations said Monday that food delivery and other aid operations had resumed, after a suspension linked to last week's fatal attack on a U.N.driver in Gaza.
But it said some 500,000 people still lack water, and urged Israel to increase the length of the daily break in fighting.
Activists attempting to deliver supplies to Gaza by boat were thwarted a second time Monday when the boat's engine failed. Activists from the U.S.-based Free Gaza were trying to bring doctors, aid workers, and supplies from Cyprus. Last month their first try failed when their boat collided with another vessel.
The aid workers were expected to re-try their trip as soon as repairs on the engine were complete.
Some information for this report was provided by AP and Reuters.