Gaza conditions at 40-year low
The groups' report, Gaza Strip: A Humanitarian Implosion, says the blockade has dramatically worsened levels of poverty and unemployment, and has led to deterioration in education and health services.
More than 1.1 million Gazans are dependent on food aid and of 110,000 workers previously employed in the private sector, 75,000 have now lost their jobs, the report says.
"Unless the blockade ends now, it will be impossible to pull Gaza back from the brink of this disaster and any hopes for peace in the region will be dashed," said Geoffrey Dennis, of Care International UK.
Last week Israeli forces launched a bloody and destructive raid in northern Gaza, in which more than 120 Palestinians - including many civilians - were killed.
Israel says the measures are designed to stamp out frequent rocket fire by Palestinian militants.
Recent rocket attacks have hit deeper into southern Israel, reaching Ashkelon, the closest large Israeli city to the Gaza Strip.
Israel says its military action and other measures are lawful and needed to stop rocket attacks from Gaza.
Israel's Defence Ministry rejected the criticism in the report, blaming the Hamas militant group which controls Gaza.