Seriously ill patients are not receiving the treatment they need. The water supply is patchy, sanitation on the point of collapse.
The ICRC statement comes as a UN Human Rights Council inquiry into alleged war crimes in Gaza and southern Israel holds public hearings in Gaza City.
South African judge Richard Goldstone's inquiry is holding two days of hearings in Gaza and will take testimony in Geneva in July.
Israel has refused to allow the investigators onto its territory and has accused the mission of bias against it.
Poverty in Gaza is at what the Red Cross calls an "alarming" level.
"The poorest residents in particular have exhausted their coping mechanisms and often have to sell off their belongings to be able to buy enough to eat," said Antoine Grand, head of the ICRC's sub-delegation in Gaza.
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