After being ordered by Israel to flee the north of the narrow coastal strip, much of Gaza’s 2.2m civilian population is now confined to the south including in UN shelters, where disease from overcrowding is a growing concern.
Under US pressure to limit the impact on civilians, Israel said it was proceeding with more targeted evacuations around specific neighbourhoods of Khan Younis.
"We're moving ahead with the second stage now. A second stage that is going to be difficult militarily," government spokesman Eylon Levy said.
One senior Israeli official warned: "We did not start this war. We regret civilian casualties but when you want to face evil, you have to operate."
Inside a ward of the Nasser hospital in Khan Younis, almost every inch of floor space was taken up by the wounded victims of Israeli bombardment.
Two young girls were being treated, still covered in dust from the collapse of the house that had buried their family. "My parents are under the rubble," sobbed one. "I want my mum, I want my mum, I want my family."
Richard Peeperkorn, the World Health Organisation representative in Gaza, said the situation for civilians around Khan Younis and the border city of Rafah was "getting worse by the hour".
He told reporters that amounts of aid reaching Gaza were "way too little" and that "we are looking at an increasing humanitarian disaster".
Peeperkorn said the WHO had complied with an Israeli order to remove supplies from warehouses in Khan Younis before the areas become subject to active combat. Israel has denied issuing such an order.
Among those fleeing the north are believed to be Hamas’s Gaza-based military and political leaders blamed by Israel for the October 7 attack that massacred 1,200 Jewish civilians and saw some 240 people taken hostage.
More than 100 of the hostages seized by Hamas and other Palestinian terror groups were freed during a seven-day truce, but the deal collapsed last Friday, and some observers see Israel rushing to complete the offensive before US pressure grows too acute for another ceasefire.
Israel accuses Hamas of putting civilians in danger by operating from populated areas, including in tunnels which can only be destroyed by large bombs.
Israeli forces have assembled a system of pumps that could be used to flood Hamas tunnels with seawater, the Wall Street Journal reported, citing US officials.
More than 700 Palestinians have been killed since Friday to add to an overall death toll of nearly 16,000, according to Gaza's Hamas-run health ministry, which does not differentiate between civilians and combatants. After weeks of disputing the ministry's figures, Israeli officials now say they are largely accurate.
Lynn Hastings, the UN’s Humanitarian Coordinator for the Occupied Palestinian Territory, said: “Nowhere is safe in Gaza and there is nowhere left to go.
“The conditions required to deliver aid to the people of Gaza do not exist. If possible, an even more hellish scenario is about to unfold, one in which humanitarian operations may not be able to respond,” she said.
“What we see today are shelters with no capacity, a health system on its knees, a lack of clean drinking water, no proper sanitation and poor nutrition for people already mentally and physically exhausted: a textbook formula for epidemics and a public health disaster.”
In London, Home Office minister Robert Jenrick said: “We have had a number of frank conversations with Israel, at every level, in which we have encouraged them to pursue this vital war in a responsible manner.”
Speaking on BBC Radio 4’s Today programme, he said the UK Government was working with aid organisations “to get as much aid and medicines into Gaza as possible”.
But the minister stressed full British support for Israel’s offensive within international law. “The eradication of Hamas will be a blessing to people in Gaza, to people in Israel and frankly to the whole world.”