Israel's bid to capture Gaza City has sparked international outrage, with the territory already devastated by nearly two years of war and gripped by a UN-declared famine.

It comes ahead of a planned move by several Western countries, including France and Britain, to recognise a Palestinian state next week at a UN summit.

The United Nations estimated at the end of August that about one million people were living in Gaza City and its surroundings. Israel says hundreds of thousands of them have fled the Gaza Strip's largest city.

In a post on X addressing residents of Gaza City, the military's Arabic-language spokesman, Avichay Adraee, said: "From this moment, Salah al-Din Road is closed for southbound travel. The Israel Defense Forces will continue to operate with unprecedented force against Hamas and other terrorist organisations." 

He added the only possible route south was via Al-Rashid street and urged residents to "take this opportunity and join the hundreds of thousands of city residents who have moved south to the humanitarian area".

Israel on Wednesday announced a "temporary" new route for residents to flee Gaza City, after it launched an intense ground offensive and massive bombardment of the Palestinian territory's main city after nearly two years of devastating war.

The military had said the transportation route via Salah al-Din street would remain open for just 48 hours from midday (0900 GMT).

Salah al-Din street is the main north-south road through the Gaza Strip.

The US-backed offensive on Gaza City began on Tuesday and came as a United Nations probe accused Israel of committing "genocide" in the Gaza Strip, saying Prime Minister Benjamin Netanyahu and other senior officials had incited the crime.

Israel rejected the findings and slammed it as "distorted and false".

AFP footage from the Al-Rashid coastal road on Thursday showed long lines of Palestinians heading south on foot or in vehicles piled high with meagre belongings.

In western Gaza City on Friday, displaced Palestinian Sami Baroud described "relentless and intense shelling".

"Our life has become nothing but explosions and danger," the 35-year-old told AFP by telephone.

"We have lost everything -- our lives, our future, our sense of safety. How can I evacuate when I can't even afford transportation?"

Umm Mohammed Al-Hattab, 49, also said her family had nowhere to go and couldn't afford the cost of moving.

"My seven children and I are still living in tents in western Gaza City after (Israel) bombed our home," she said.

"The bombing hasn't stopped, and at any moment, we expect a missile to fall on us. My children are terrified, and I don't know what to do," she said.

Hamas's October 7, 2023 attack on Israel which sparked the war resulted in the deaths of 1,219 people, most of them civilians, according to an AFP tally of official figures.

Israel's retaliatory campaign has killed at least 65,141 people, also mostly civilians, according to figures from the territory's health ministry that the United Nations considers reliable.