The Israeli military says the raid, now in its fifth day, is intended to stop Hamas fighters staging further attacks from Jabalia and to prevent them regrouping.
It has repeatedly issued evacuation orders to residents of Jabalia and nearby areas, but Palestinian and UN officials say there are no safe places to flee to in the Gaza Strip.
The Palestinian Civil Emergency Service said it had received unconfirmed reports that dozens of Palestinians might have been killed in Jabalia and other areas of northern Gaza, but is unable reach them because of Israeli bombardments.
"At least 400,000 people are trapped in the area," Philippe Lazzarini, the head of the UN aid agency for Palestinian refugees, UNRWA, posted on X on Wednesday.
Northern — Philippe Lazzarini (@UNLazzarini) #Gaza: no end to hell. At least 400,000 people are trapped in the area. Recent evacuation orders from the Israeli Authorities are forcing people to flee again & again, especially from Jabalia Camp. Many are refusing because they know too well that no place anywhere…October 9, 2024
"Recent evacuation orders from the Israeli Authorities are forcing people to flee again & again, especially from Jabalia Camp.
"Many are refusing because they know too well that no place anywhere in #Gaza is safe."
Lazzarini said some UNRWA shelters and services were being forced to shut down for the first time since the war began and that with almost no basic supplies available, hunger was spreading again in northern Gaza.
"This recent military operation also threatens the implementation of the second phase of the #polio vaccination campaign for children," he said.
Israel did not immediately comment on Lazzarini's remarks.
Israeli authorities have previously said they facilitate food deliveries to Gaza despite challenging conditions.
The Gaza health ministry said the army had ordered three hospitals in northern Gaza to evacuate.
Hundreds of patients and medics were trapped inside those facilities, it said in a statement on Wednesday.
Israel's military, which is now also in conflict with Hezbollah in Lebanon, says Hamas militants use residential areas as cover in densely populated Gaza, including schools and hospitals. Hamas denies this.
Hamas exiled official Izzat El-Reshiq said in a statement Israel's escalation in northern Gaza aimed to punish residents for refusing to leave their homes.
He blamed the United States for being partners with Israel in the "war of genocide" in Gaza.
In one Israeli strike overnight on a house in Shejaia, a suburb of Gaza City, nine people of the same family were killed, medics said.
Others were killed overnight in central areas of the Gaza Strip.
Israel began its offensive against Hamas in Gaza after fighters from the Palestinian militant group attacked southern Israeli communities on October 7, 2023, killing about 1200 people and taking about 250 hostage, according to Israeli tallies.
Nearly 42,000 Palestinians have been killed in the Israeli offensive, the Gaza health ministry says.
Most of Gaza's 2.3 million people have been displaced and much of the enclave has been laid to waste.
