Organisations in Gaza and eyewitnesses say looting has continued for several nights by unidentified, armed and unarmed individuals.
They've broken into the warehouses of the United Nations, aid groups and commercial entities as well as bakeries and shops.
Israel has blocked any humanitarian aid from entering the territory since Prime Minister Benjamin Netanyahu ended the ceasefire with Hamas in March, throwing Gaza into what is believed to be the worst humanitarian crisis in nearly 19 months of war.
The UN High Commissioner for Human Rights previously warned that starving civilians, as a military tactic, constitutes a war crime.
Israel has said the blockade and its renewed military campaign are intended to pressure Hamas to release the remaining 59 hostages it still holds and to disarm the Palestinian militant group.
Aid groups have warned that Gaza's civilian population is facing starvation, and there is concern that the desperation could lead to a breakdown of law and order.
While there have been incidents of looting by armed gangs throughout the war, aid workers say this week's incidents mark an escalation, with it being more splintered, less organised and reaching urban areas.
The ransacking in Gaza City began Wednesday evening after reports that aid trucks had entered the north from the south, said one aid worker who was not authorised to speak to the media.
A security report circulated among aid agencies that night, saying a group of armed people forcefully broke into a bakery driven by rumours of stored food supplies.
The storage was empty and the group moved to a soup kitchen affiliated with an international aid group in the Al-Shati camp and looted it, said the report.
The United Nations Relief and Works Agency said its staff were safely evacuated after thousands of Palestinians breached its Gaza City field office Wednesday evening and took medications.
Louise Wateridge, a senior emergency officer at UNRWA, called the looting "the direct result of unbearable and prolonged deprivation".
The ransacking continued through Friday night.
Three witnesses told the AP that dozens of armed men stormed into at least two UN warehouses, pushing past police and local security guards protecting the facilities.
"There were organised gangs," said Ahmed Abu Awad, a resident of western Gaza City, where some of the looting took place.
Yahya Youssef, another witness, said he saw dozens of armed men on the streets in western Gaza City, in gunfights for two consecutive nights, with policemen and security forces that protect UN and aid groups' facilities.
Both men said Israeli drones and aircraft were flying over the area while looting was underway.
An Israeli strike Friday night killed three people, including two tasked with guarding the area in western Gaza City and a child, said a statement from the Hamas-run interior ministry. Staff at Al-Shifa hospital, which received the bodies, also confirmed the deaths.
The Israeli military said it could not comment on the strike without being provided with the exact coordinates of the incident.
The Gaza Interior Ministry said on Saturday it killed six suspects and wounded 13 others with gunshots to the legs in the past two days over looting activities.
The ministry also enforced a night curfew starting on Friday in some of Gaza City's main streets.
Israeli strikes on Gaza continued overnight Friday, leaving at least 17 people dead, including children, in the southern City of Khan Younis, according to hospital records.
Among the dead were 11 people from the same family, according to Nasser Hospital, which received the bodies.
Another strike killed two newly married couples, said one of their families.
