The UN says hundreds of thousands of people in the territory are at growing risk of famine.
People living in the isolated north of Gaza have told the BBC that children are going without food for days, as aid convoys are increasingly denied permits to enter. Some residents have resorted to grinding animal feed into flour to survive, but even stocks of those grains are now dwindling, they say.
People have also described digging down into the soil to access water pipes, for drinking and washing.
The UN has warned that acute malnutrition among young children in the north has risen sharply, and is now above the critical threshold of 15%.
The UN's humanitarian coordination agency, Ocha, says more than half the aid missions to the north of Gaza were denied access last month, and that there is increasing interference from Israeli forces in how and where aid is delivered.