A report by the 29 NGOs, including Save the Children, Oxfam and Care, said that humanitarian aid entering the Palestinian territory had fallen to an all-time low, averaging 37 humanitarian trucks per day in October, and 69 in the first week of November.
This compared with an average of 500 a day before the October 7, 2023, unprecedented attack by Hamas militants on Israel.
The NGOs said that "merely counting the number of trucks" was no longer an adequate measure of gauging the amount of aid reaching the people in the Gaza Strip.
"Looting is an ongoing issue," they said, calling the theft of goods "a consequence of Israel's targeting of the remaining police forces in Gaza" as well as of scarcity of essential goods, lack of routes and the closure of most crossing points which had resulted in "desperation of the population amid those dire conditions".
Based on "media reports", the NGOs accused Israel's military of "failing to prevent aid trucks from being looted and armed gangs from extorting aid organisations for protection money".
In "some cases", the report said, "the remaining members of local police forces tried to take action against the looters, but were attacked by Israeli troops".
Incidents had taken place "close by or in full view of Israeli forces without them intervening, even when truck drivers asked for assistance", it said.
Meanwhile, Israeli air strikes had killed at least 20 aid workers from mostly Palestinian organisations between October 10 and November 13, the report said.
"Staff were killed in their homes, in displacement camps and while delivering life-saving aid," it said.
On Tuesday, Israel announced the opening of an additional aid crossing into Gaza, on the eve of a US deadline to boost relief deliveries, but aid agencies said it was not enough.
The United States last month warned Israel to improve the humanitarian conditions in Gaza or risk a cut to its military support.
A day before the deadline, the Israeli military said it opened the Kissufim crossing "as part of the effort and commitment to increase the volume and routes of aid" to Gaza.
But the UN agency for Palestinian refugees (UNRWA) and eight humanitarian groups said Israel was still not doing enough to get aid in.
US Secretary of State Antony Blinken and Defense Secretary Lloyd Austin warned Israel last month it had 30 days to ramp up Gaza aid deliveries or risk losing some military assistance from Washington, its chief arms supplier.
