Dozens of Israeli tanks as well as armoured personnel carriers and bulldozers entered the south of the territory near the city of Khan Yunis, which is crowded with internally displaced Palestinians, witnesses told AFP.

Amin Abu Hawli, 59, said the Israeli vehicles were "two kilometres (1.2 miles) inside" Gaza in the village of al-Qarara, while Moaz Mohammed, 34, said Israeli tanks were rolling down the strip's main north-south highway, the Salah al-Din road.

"They are holding Salah al-Din road on both sides and are now cutting it between Deir al-Balah (in central Gaza) and Khan Yunis, firing bullets and tank shells at cars and people trying to move through the area," he said.

Weeks after Israel sent ground forces and tanks into northern Gaza, the army has been air-dropping leaflets in the besieged territory's south, especially around Khan Yunis, telling Palestinians there to flee to other areas.

Full-scale fighting resumed Friday after the collapse of a week-long truce brokered by Egypt, Qatar and the United States, during which Israel and Hamas had exchanged scores of captives and prisoners.

Air strikes have since intensified in Gaza's south, said James Elder, a spokesman for the United Nations children's agency UNICEF.

"Despite what has been assured, attacks in the south of Gaza are every bit as vicious as what the north endured," he posted Monday on X, formerly Twitter.

"Somehow, it's getting worse for children and mothers."

In its latest estimate, the UN humanitarian agency OCHA said around 1.8 million people in Gaza, roughly 75 per cent of the population, had been displaced, many to overcrowded and unsanitary shelters.

Many people have been forced to flee to the south of the Gaza Strip and fear being pushed towards the border with Egypt.

Many Palestinians fear a repeat of the displacement of 760,000 Palestinians (Nakba) that took place 75 years ago.