The UN Relief and Works Agency for Palestine Refugees in the Near East (UNRWA) said it is unprecedented for its warehouses to be empty of food.
"It's been a week since we've been able to get any food supplies into Gaza, which has caused us to fall into this particular crisis," John Ging, the head of UNRWA in Gaza, told UN Radio.
"We have quite simply run out because again we haven't been allowed for many months to build up a reserve and that's why we are in such a precarious situation. This evening, our stores are now empty and we won't be able to resume our food distribution until such time as we get a re-supply together," he added.
"It's very harrowing for the population here, not just physically but psychologically as well."
All Gaza commercial crossings remained closed today for the eighth day in row, with no humanitarian or commercial goods being allowed in.
UNRWA said it is not clear when the crossings will reopen or when it will be able to resume its distributions. It stressed that "having hundreds of thousands of hungry and desperate people in Gaza is not in the interests of anyone who believes in peace."
Meanwhile, the Office of the UN Special Coordinator for the Middle East Peace Process (UNSCO) reports that fuel was prevented from entering Gaza today, with the Israeli Government citing as its reason the firing of mortars and rockets into Israel.
As a result, Gaza's power plant will shut down today and probably remain closed until Sunday. Supplies of diesel and petrol are also running low, according to UNSCO.