The United Nations and International Committee of the Red Cross (ICRC), concerned at escalating Middle East violence, called on Israel on Friday to allow urgent medical and food supplies into Gaza.
Many Palestinian civilians - confined by the closure of key crossing points and suffering from a clampdown on foreign aid - are now living on "just one meal a day", according to the UN's World Food Programme (WFP).
The international aid agencies said Israeli air strikes have knocked out water systems and a major power transformer, cutting vital electricity supplies to hospitals as well as families.
WFP spokesman Simon Pluess told a news briefing that the crisis had affected all aspects of Palestinian life, including access to food, health care, education and fuel.
Dorothea Krimitsas, ICRC spokeswoman, said the Geneva-based agency was negotiating with Israel to allow the passage of humanitarian aid, including essential medicines and medicial supplies for the Palestinian Red Crescent.