Israel's ultimatum that over one million people in northern Gaza should relocate within 24 hours is "extremely dangerous" and "simply not possible", UN chief Antonio Guterres has said, asserting that "even wars have rules.” UN officials in Gaza on Thursday were informed by their liaison officers in the Israeli military that the entire population of northern Gaza, approximately 1.1 million, should relocate to the southern part within the next 24 hours.

The same order applied to all UN staff and those sheltered in UN facilities – including schools, health centres and clinics.

“Moving more than one million people across a densely populated warzone to a place with no food, water, or accommodation, when the entire territory is under siege, is extremely dangerous – and in some cases, simply not possible,” Guterres told reporters here on Friday.

The UN Secretary-General made those remarks before heading to a Security Council meeting on the situation in the Middle East.

He said that after days of airstrikes, the Israeli Defense Forces have ordered the Palestinians in Gaza and its surroundings to move to the south of the territory.

Voicing his deep concern, the UN chief said that the “hospitals in the south of Gaza are already at capacity and will not be able to accept thousands of new patients from the north.” The health system is also on the "brink of collapse” and “morgues are overflowing,” he said.

Guterres said 11 healthcare staff have been killed while on duty and there have been 34 attacks on health facilities in the past few days.

Describing the situation in Gaza as reaching a “dangerous new low,” he said the entire territory faces a water crisis as infrastructure has been damaged and there is no electricity to power pumps and desalination plants.

Asserting that “even wars have rules”, Guterres said there is an immediate need for humanitarian access throughout Gaza for the UN to "get fuel, food and water to everyone in need." "International humanitarian law and human rights law must be respected and upheld; civilians must be protected and never used as shields. All hostages in Gaza must be released immediately,” he said.

Guterres underscored that it is imperative that all parties – and those with influence over them – do everything possible to achieve these steps.

The "horrific terror attacks” by Hamas on Israel killed more than 1,200 people and injured thousands more last Saturday. These were followed by intense bombardment of Gaza that has already killed 1,800 people, and injured thousands more, the UN chief said.

UN Under-Secretary-General for Humanitarian Affairs and Emergency Relief Coordinator Martin Griffiths described Israel’s ultimatum as a noose tightening around Gaza’s civilian population.

“The noose around the civilian population in Gaza is tightening. How are 1.1 million people supposed to move across a densely populated warzone in less than 24 hours? I shudder to think what the humanitarian consequences of the evacuation order would be,” Griffiths said.

Stephane Dujarric, spokesman for Guterres, told reporters on Friday that the UN considers it is "impossible" for such a movement to take place without devastating humanitarian consequences.

"We strongly appeal for any such order to be rescinded. It could transform what is already a tragedy into a calamitous situation,” he said.

Dujarric said the Secretary-General and his team have been “working the phones” and he is in constant contact with Israeli authorities, urging them to avert a humanitarian catastrophe.

“We need to ensure full support for opening humanitarian access to the Gaza Strip to prevent a further loss of civilian lives. It is vital that Israeli Authorities protect all civilians in UNRWA shelters including schools and protect all civilians, full stop," Dujarric said.

He said the UN facilities must be protected at all times and must never come under attack, in accordance with international humanitarian law.

UN agencies and human rights organisations voiced deep concern over Israel’s ultimatum, describing it as “outrageous”.

The UN Country Team in Palestine called on the Israeli government to rescind its announcement for UN agencies and Palestinians to relocate to southern Gaza without any guarantee for their safety or their return.

“Palestinian civilians, including women and children, are terrified, injured, and traumatized. This will cause a humanitarian tragedy that can and must be averted,” it said.

The agency said one million people cannot flee in a day and many were already displaced or do not have vehicles, and could not move while bombings continued.

“Mass displacement puts the lives of the sick and wounded in immediate danger and risks a public health disaster, at a time when the health system is on the brink of collapse; hospitals in the south of the Gaza Strip are at capacity and unable to accept new patients,” it added.

The UN agency said international law means Israel needs to take precautionary measures in future attacks to limit the harm to civilians and civilian objects.

The World Health Organization joined the wider United Nations in appealing to Israel to immediately rescind orders for the evacuation of over 1 million people living north of Wadi Gaza.

“A mass evacuation would be disastrous—for patients, health workers and other civilians left behind or caught in the mass movement,” the global health agency said. With ongoing airstrikes and closed borders, civilians have no safe place to go. Almost half of the population of Gaza is under 18 years of age, it said.

"With dwindling supplies of safe food, clean water, health services, and without adequate shelter, children and adults, including the elderly, will all be at heightened risk of disease,” it said.

The Palestinian Ministry of Health has informed WHO that it is impossible to evacuate vulnerable hospital patients without endangering their lives.

“Vulnerable patients include those who are critically injured or dependent on life support. Moving them amid hostilities puts their lives at immediate risk,” WHO said.

Doctors Without Borders/Médecins Sans Frontières (MSF), the international medical humanitarian organisation, has around 300 people working with it as staff in Gaza and termed the Israeli government’s 24-hour notice as “outrageous”.

“This represents an attack on medical care and on humanity. We are talking about more than a million human beings. 'Unprecedented' doesn’t even cover the medical humanitarian impact of this.

"Gaza is being flattened, thousands of people are dying. This must stop now. We condemn Israel’s demand in the strongest possible terms,” MSF General Director Meinie Nicolai said.

The United Nations Relief and Works Agency for Palestine Refugees in the Near East (UNRWA) noted that since October 7, over 423,000 people have already been displaced. Of them, more than 270,000 have taken refuge in UNRWA shelters.

UN Women reports that Gaza is home to 50,000 pregnant women who are struggling to access essential health services as healthcare workers, hospitals and clinics come under attack. Some 5,500 of these women are due to give birth in the coming month.

Except for the headline, this story has not been edited by The Telegraph Online staff and has been published from a syndicated feed.