Thousands of Palestinians fled Saturday to southern Gaza seeking refuge after Israel warned them to evacuate before an expected ground offensive against Hamas.

Prime Minister Benjamin Netanyahu warned that nearly a week of fierce bombardment was "just the beginning", as Israel seeks to retaliate against an attack that killed more than 1,300 a week ago - the deadliest attack in Israel's history. 

On Friday, the United Nations said Israel had given people in Gaza 24 hours to evacuate - a deadline that drew criticism from various quarters, including EU top foreign affairs official Josep Borell, who said it would be "utterly impossible to implement". 

Israel did not confirm that deadline but later said that it would take some more time to amass the necessary troops for the offensive. 

Israel's army said its ground forces made "localised" raids into Gaza in the past 24 hours "to cleanse the area of terrorists and weaponry" and try to find "missing persons".

Most of those killed when militant fighters burst through the heavily militarised border into Israel last Saturday were civilians, in an attack compared to 9/11 in the United States.

At least 1,900 Gazans -- most of them civilians and including more than 600 children -- have been killed in missile strikes on the densely populated enclave, the health ministry said.

"Where to go?" asked Umm Hossam, 29, who was among the thousands fleeing. 

An Israeli army Merkava battle tank deploys with others along the border with the Gaza Strip. Photo: AFP

"How long will the strikes and death last? We have no homes left, every area of Gaza is under threat," said the 29-year-old, her face streaked with tears,

Hamas took about 150 Israeli, foreign and dual national hostages back to Gaza in the initial attack, Israel has said.

The militant group said Friday that 13 of them had been killed in Israeli air strikes. 

'Genocide'

German Foreign Minister Annalena Baerbock, in Israel Friday, accused Hamas of using residents as a "shield" in Gaza, where Israel has cut off water, fuel and food supplies.

US President Joe Biden spoke with the families of 14 Americans who have been missing since the Hamas attack Friday.

"We're going to do everything in our power to find them," he told CBS's "60 Minutes". 

He also stressed that addressing the swelling humanitarian crisis in Gaza was a "priority".

"The overwhelming majority of Palestinians had nothing to do with Hamas and Hamas's appalling attacks, and they're suffering as a result as well," Biden said in a speech.

Tensions have risen across the Middle East and beyond, with angry protests in support of the Palestinians, while Israel faces the threat of a separate confrontation with Hezbollah in Lebanon. 

A Reuters video journalist was killed and six other reporters -- from AFP, Reuters and Al Jazeera -- were injured in southern Lebanon close to Israel, caught up in cross-border shelling.

Palestinians carry their belongings as they try to flee the devastation in Gaza. Photo: AFP

In the occupied West Bank, at least 16 Palestinians were killed in clashes with Israeli forces during protests supporting Gaza, the health ministry said.

Palestinian Prime Minister Mohammad Shtayyeh accused Israel of committing "genocide" in Gaza.

But Netanyahu's spokeswoman Tal Heinrich told AFP: "Everything that happens in Gaza is Hamas's responsibility."

Thousands also demonstrated in support of the Palestinians on Friday in Beirut, Iraq, Iran and in Jordan.

Demonstrations also took place in Bahrain, where US Secretary of State Antony Blinken was visiting Saturday, as part of a regional tour seeking to keep calm in the Arab world.

'Impossible'

In Gaza, UN officials said the Israeli military, whose troops are massing at the border, had said some 1.1 million people in the north of the enclave needed to evacuate to the south "within the next 24 hours".

Israel did not confirm it had set the deadline, but later admitted it would take more time. A ground offensive would be complicated by the presence of hostages.

The United Nations described the immediate movement of nearly half of the 2.4 million in the Gaza Strip as "impossible" called for the evacuation order to be rescinded.

"Moving more than one million people across a densely populated war zone to a place with no food, water, or accommodation, when the entire territory of Gaza is under siege, is extremely dangerous – and in some cases, simply not possible," UN chief Antonio Guterres said on X, formerly Twitter.

Hospitals are struggling to cope with the dead and wounded  and the health system was "at a breaking point", the World Health Organization said.

EU High Representative for Foreign Affairs Josep Borell also criticised the Israeli plan.

"I am saying that, representing the official position of the European Union,... (the evacuation plan) is utterly, utterly impossible to implement," Borrell told a press conference in Beijing on the final day of a three-day diplomatic visit to China.

"To imagine that you could move one million people in 24 hours in a situation like Gaza can only be a humanitarian crisis," he added.

Even as Borell was speaking, EU Commission President Ursula von der Leyen and European Parliament President Roberta Metsola were touring Israel and pledging solidarity with the country, further illustrating the EU's unclear position concerning the ongoing conflict. 

In Jordan, after a meeting with Blinken, King Abdullah II called for "humanitarian corridors" to be opened urgently.

Egypt -- which runs the Rafah crossing to the south of Gaza -- faces a dilemma of accepting refugees with the possibility that Israel may never let them return, weakening Palestinian aspirations for statehood.

Air strikes

AFP correspondents in Gaza said the Israeli military on Friday dropped flyers warning residents to flee "immediately" south of Wadi Gaza, with a map pointing south across a line in the centre of the 40 kilometre-long (25 mile-long) territory. 

The army said it "will continue to operate significantly in Gaza City and make extensive efforts to avoid harming civilians".

Families carry their belongings - and children - away from northern Gaza. Photo: AFP

"Hamas terrorists are hiding in Gaza City inside tunnels underneath houses and inside buildings populated with innocent civilians." 

Netanyahu has vowed to "crush" Hamas, and has likened it to the Islamic State group.

But in Geneva, the Red Cross said the unjustifiable "horrific" attacks on Israel could equally not justify "the limitless destruction of Gaza".

A 'crime'

Hamas has said Palestinians rejected the evacuation request, yet thousands of Gazans were on the move in search of safety, carrying plastic bags of belongings, suitcases on their shoulders and children in their arms.

Even before the evacuation order, more than 423,000 people had already fled their homes in Gaza, according to the UN.

Arab League chief Ahmed Abul Gheit said Israel's evacuation order is a "forced transfer" that constitutes "a crime". 

The bodies of Israeli casualties, stored at an army base in Ramla. Photo: AFP

Palestinian president Mahmud Abbas said it will be "tantamount to a second Nakba" or "catastrophe", referring to the 760,000 Palestinians who fled or were expelled from their homes during the 1948 war that accompanied Israel's creation.

Russian President Vladimir Putin warned that Israel risked waging an "unacceptable" siege in Gaza comparable to the Nazi blockade of Leningrad during World War II.

Mass killings

Israeli soldiers have swept the southern towns and kibbutz farming communities since last Saturday.

They said they found the bodies of 1,500 militants, as well as large numbers of civilians killed by Hamas fighters.

Yossi Landau, with the Zaka organisation that recovers the bodies of people who suffer unnatural deaths, said he found a dead woman with her stomach "ripped open, a baby was there, still connected with the cord, and stabbed". 

They were among more than 100 people killed in Beeri, just outside Gaza, while around 270 were gunned down or burned in their cars at the nearby Supernova music festival.

Hamas has denied that its fighters killed infants.

Hezbollah threat

Israel faces a potential second front in the north after the Iran-backed Hezbollah group in Lebanon said it was "fully prepared" to join Hamas in the war when the time was right.

There has been cross-border fire in recent days, sparking concern about regional stability and prompting the United States to send additional munitions and its largest aircraft carrier.

Israeli forces said Saturday said they had "struck a Hezbollah terror target in southern Lebanon" in response to a drone crossing the border. 

Biden has warned other regional powers not to get involved. 

Israel's arch foe Iran has long financially and militarily backed Hamas and praised its attack, but insists it was not involved.