Israeli tanks advanced into the fringes of Gaza City on Monday, witnesses said, as it ramped up its war on Hamas saying it had killed dozens of militants in hundreds of strikes. 

"We have hit more than 600 targets in the past 24 hours," a military spokesperson told AFP, up from 450 the previous day, with Hamas militants also reporting "heavy fighting" in northern Gaza.

Tanks entered the Zaytun district on the southern fringes of Gaza City, cutting a key road from the north to the south of the war-torn Palestinian territory, witnesses told AFP on Monday. 

"They have cut the Salahedin Road and are firing at any vehicle that tries to go along it," said one resident who did not give his name.

Israel has on several occasions warned the 1.1 million people living in northern Gaza, including Gaza City, to head south to avoid its military strikes as it pushes ahead with a mission to "destroy" the territory's Hamas rulers.

Although huge numbers have left in recent weeks, tens of thousands more are believed to be still in the zone. 

Since Friday, Israeli forces have stepped up their ground offensive as part of the military response to the October 7 Hamas attacks that officials say killed 1,400 people, mostly civilians, with another 239 people taken hostage.

The health ministry in Hamas-run Gaza says more than 8,000 people, mainly civilians, mostly civilians and more than half of them children, have since been killed in Israeli air and ground strikes.

The Israeli army said troops killed "dozens" of militants in overnight clashes, saying they had "barricaded themselves inside buildings and tunnels and attempted to attack the troops".

In one incident, a fighter jet targeted a building "with over 20 Hamas terrorist operatives inside," while another fighter jet was guided to an anti-tank missile launching post in the area of Al-Azhar University, it said. The university is in the heart of Gaza City.

It also said it hit "weapons depots, dozens of anti-tank missile launching positions, as well as hideouts and staging grounds used by the Hamas terrorist organisation".