Palestinians carried belongings through the rubble-strewn streets of Gaza City Friday in search of refuge as Israel's army warned residents to flee immediately before an expected ground offensive in retaliation against Hamas for the deadliest attack in Israeli history.

Hamas fighters broke through the militarised border barrier around the Gaza Strip enclave last Saturday, killing more than 1,300 people in Israel, in an attack compared to 9/11 in the United States.

There have been protests in support of the Palestinians across the Middle East and beyond, plus threats of a further confrontation between Israel and Hezbollah in neighbouring Lebanon.

At least five Palestinians were killed by Israeli fire across the occupied West Bank during rallies in solidarity with Gaza, the health ministry said.

In Gaza, United Nations officials said the Israeli military told them the evacuation should be carried out "within the next 24 hours" but the army did not confirm that timeline.

Israel has retaliated to Hamas's attacks by hitting targets in Gaza with thousands of munitions. The strikes have claimed more than 1,530 lives -- 500 of them children, according to the health ministry in Gaza, where the health system is "at a breaking point," the World Health Organization said.

"One million people no food no water, and still they are bombing them as they leave. Where are we going to put them?" Elizabeth El-Nakla, the mother-in-law of Scotland's First Minister Humza Yousaf, said in a video he posted.

"This will be my last video. Everybody from Gaza is moving towards where we are," added Nakla, who was visiting relatives in Gaza from Scotland.

"May God help us."

The UN said the "impossible" mass relocation would affect 1.1 million or about half the entire population of the Gaza Strip, and urgently appealed for the order to be rescinded.

- Hostages -

Any Israeli ground operation is complicated by Hamas's holding -- according to Israel's government -- an estimated 150 Israeli, foreign and dual-national hostages who were taken back to Gaza during the attack.

Hamas on Friday said 13 hostages, including foreigners, had been killed in Israeli strikes. The militants, listed as a terrorist organisation by the United States and Europe, had previously reported four hostages killed in strikes.

AFP correspondents in Gaza said the Israeli military on Friday dropped flyers on Gaza 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 miles) territory.

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

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

AFP correspondents said there were "heavy strikes" in the northern Gaza Strip on Friday morning, including Al-Shati refugee camp and Gaza City, primarily targeting residential buildings.

The Hamas media office reported Israeli air raids on Khan Yunis and Rafah in the south.

Israel's army said its "fighter jets struck 750 military targets in the northern Gaza Strip overnight" including "residences of senior terrorist operatives used as military command centres".

Israeli Prime Minister Benjamin Netanyahu said Hamas "will be crushed." The militants, who want Israel's destruction, said Saturday's attack sought to end Israel's "rampaging without being held accountable".

Hamas, in a statement, said "our Palestinian people" rejected Israel's Gaza evacuation order.

- A 'crime' -

Carrying plastic bags of belongings, with suitcases on their shoulders and children in their arms, Gazans were, however, moving to other areas of the crowded territory in search of safety on Friday.

Some walked while others drove, with belongings strapped to the roofs of their vehicles.

More than 423,000 people have already fled their homes in the territory of 2.4 million, according to the UN.

Such an evacuation order could transform "what is already a tragedy into a calamitous situation," a UN spokesman said.

The territory was already under a land, air and sea blockade since 2006.

Israel has now cut off water, food and power supplies to Gaza in a total siege it has vowed will not end until all hostages are freed.

"I condemn this siege because you have to, when they ask so many people to leave, when they don't have access to food and medicine," said Norway's Foreign Minister Anniken Huitfeldt.

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

Palestinian president Mahmud Abbas meanwhile 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 coincided with Israel's creation.

Israeli army spokesman Daniel Hagari told reporters: "We are trying to provide the time and we are doing a lot of effort, and we understand it won't take 24 hours."

Gaza's 2.4 million residents are enduring the fifth war in 15 years.

Israeli fighter jets and drones have levelled entire blocks and destroyed thousands of buildings.

Hamas has threatened to kill captives if Israel bombs Gaza civilian targets without advance warning.

US Secretary of State Antony Blinken was in Jordan Friday, where he discussed with King Abdullah II "ways to address the humanitarian needs of civilians in Gaza while Israel conducts legitimate security operations", State Department spokesman Matthew Miller said.

King Abdullah called for "opening humanitarian corridors to allow for the entry of urgent medical and relief aid to Gaza", a royal court statement said.

The top US diplomat, on a regional tour, arrived from Israel which he visited Thursday in a sign of solidarity.

Ashraf al-Qudra, a spokesman for the health ministry in Hamas-controlled Gaza, said in a statement posted on Telegram that "hospitals are starting to lose capacity" in a worsening situation with medicine and fuel running out.

- Military build-up -

Israel has called up 300,000 reservists and moved forces, tanks and armour to the southern desert area around Gaza.

On Friday an AFP correspondent near Sderot, just outside Gaza, saw a convoy of more than 20 Israeli tanks and a dozen armoured vehicles heading toward Gaza.

In fields along the border with the territory, artillery fires like clockwork with a deafening noise every 30 seconds towards barely visible targets in Gaza, shaking the earth.

Since Saturday Israeli soldiers have swept the southern towns and kibbutz communities and said they found the bodies of 1,500 militants, while making ever more shocking discoveries of large numbers of dead civilians.

- Hezbollah threat -

Israel's war now flaring in the south is further complicated by a threat from the Hezbollah group based to the north in Lebanon.

The army and Hezbollah have exchanged cross-border fire in recent days.

A Hezbollah official said on Friday his movement was "fully prepared" to join Hamas in the war against Israel when the time is right.

The US has sent additional munitions to Israel and deployed an aircraft carrier battle group to the eastern Mediterranean in a show of support, while warning Israel's other enemies not to enter the war.

On Friday Defence Secretary Lloyd Austin, also on a solidarity visit to Israel, said Hamas fighters took "evil to another level".

He pledged "iron-clad" backing for Israel in its war.

In London, the UK said it was sending two Royal Navy ships and surveillance aircraft to the eastern Mediterranean to support Israel and "ensure regional stability".

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

The Washington Post reported that US and Qatari officials have agreed to prevent Iran from using a $6 billion humanitarian assistance fund, following the Hamas attack.

But an Iranian official said the US "can NOT renege on the agreement."

Thousands of Iranians, Iraqis and Jordanians took to the streets on Friday in a sign of support for the Palestinians.

Pro-Palestinian rallies also occurred in Asia, including in Indonesia, Pakistan, Sri Lanka, New Delhi and Dhaka.