Thousands of reservists have begun reporting for duty as the Israeli military presses ahead with its offensive to conquer Gaza City.

Ground forces are already pushing into the outskirts of Gaza’s largest urban area, which the military has said is a stronghold of Hamas.

The city is also coming under heavy Israeli aerial and artillery bombardment, with local hospitals saying that more than 50 Palestinians have been killed there since midnight.

The military has ordered residents to evacuate and head south immediately. The UN says an estimated 20,000 have done so over the past two weeks, but almost a million remain.

UN humanitarian officials have warned that the impact of a full-blown offensive would be “beyond catastrophic”, not only for those in the city but for the entire Gaza Strip.

Last month, the Israel Defense Forces (IDF) said about 60,000 reservists would be called up ahead of “Operation Gideon’s Chariots II” – the next phase of the ground offensive that it launched in May and has seen it take control of at least 75% of Gaza.

It also extended the service of 20,000 reservists who had already been mobilised.

On Tuesday, an Israeli military official said thousands had begun reporting for duty.

Israeli media said many of the reservists would be deployed to the occupied West Bank and northern Israel to free up active-duty personnel for the offensive.

They also reported that some combat units were seeing lower turnout than for previous call-ups, with reservists who had already served several tours during the 22-month war requesting exemptions for personal or financial reasons.

Prime Minister Benjamin Netanyahu announced that Israel would conquer all of Gaza after indirect talks with Hamas on a ceasefire and hostage release deal broke down in July.

At a government meeting on Sunday, he said the security cabinet had agreed the IDF’s objectives were “defeating Hamas and releasing all of our hostages”.

The armed group is currently holding 48 hostages, 20 of whom are believed to be alive.

The hostages’ families fear the new offensive will endanger them and are demanding the prime minister negotiate an agreement that would secure their release.

“Stop the war and bring all the hostages home in a deal – the living and the dead alike – some for rehabilitation in their families’ embrace, others for proper burial on Israeli soil,” said the daughter of Ilan Weiss, one of the two hostages whose bodies were recovered by Israeli troops in Gaza last week, at his funeral in Kibbutz Be’eri on Monday.

The IDF’s Chief of Staff, Lt Gen Eyal Zamir, has urged Netanyahu to accept a current proposal from regional mediators that would see about half of them released during a 60-day truce. However, the prime minister has said Israel will only accept a comprehensive deal that would see all the hostages freed and Hamas disarmed.

There were reportedly angry exchanges between Zamir and ministers at a meeting on Sunday.

The general warned that their Gaza City plan would put the hostages at risk and lead to Israel establishing a military government there, according to Israeli media. One unnamed senior minister was quoted by the Ynet website as saying that the general “did everything to convince against the plan, but made it clear several times that he would carry it out”.

In an address to reservists at Nachshonim base in central Israel on Tuesday, Zamir declared that the IDF was preparing for nothing less than “decisive victory”.

“We are going to increase and enhance the strikes of our operation, and that is why we called you,” he said. “We will not stop the war until we defeat this enemy.”

On the ground in Gaza on Tuesday, hospital officials said Israeli strikes and fire had killed at least 95 Palestinians since midnight.

Al-Shifa hospital in Gaza City reported 35 of the deaths, including nine people who were killed in an air strike in the southern Tal al-Hawa neighbourhood and seven others killed in a strike on a house in the northern neighbourhood of Sheikh Radwan.

The UN has warned that forcing hundreds of thousands of people to move further south is “a recipe for further disaster and could amount to forcible transfer”, which would be a war crime.

Global food security experts have confirmed that a famine is occurring in Gaza City and projected that it will expand to the central city of Deir al-Balah and the southern city of Khan Younis by the end of September.

The UN has also said tent camps for the displaced in the south are overcrowded and unsafe, and that southern hospitals are operating at several times their capacity.

In Khan Younis on Tuesday, Nasser hospital said it had received the bodies of 31 people killed by Israeli fire, including 13 who died in two strikes in al-Mawasi and Khan Younis camp.

Medics in the hospital’s emergency department told the BBC that most of the casualties being treated were children and elderly.

“We can’t deal with any more cases due to high pressure on us and lack of supplies. The CT [scanner] is now broken down, so we are working blindly,” one doctor said. “The current situation is catastrophic.”

Gaza’s Hamas-run health ministry meanwhile said that 13 Palestinians, including three children, had died as a result of malnutrition across the territory over the past 24 hours. That increased the total reported during the war to 361, including 185 in August alone, it added.

The UN has said the famine is a “man-made disaster” and said Israel is obliged under international humanitarian law to ensure food and medical supplies for Gaza’s population.

Israel has said there are no restrictions on aid deliveries and has disputed the health ministry’s figures on malnutrition-related deaths.

The Israeli military launched a campaign in Gaza in response to the Hamas-led attack on southern Israel on 7 October 2023, in which about 1,200 people were killed and 251 others were taken hostage.

At least 63,633 people have been killed in Gaza since then, according to the territory’s health ministry.