Officials say Palestinians are fleeing parts of Gaza City after the Israeli military began the first stages of a planned ground offensive.
Israel’s troops have established a foothold on the outskirts of the city, which is home to more than a million Palestinians after days of intense bombing and artillery fire.
It has prompted UN Secretary General António Guterres to renew calls for an immediate ceasefire to avoid the death and destruction an assault would inevitably cause.
Israel wants to signal that it is pressing ahead with its plan to capture all of Gaza City despite international criticism.
Hundreds of Palestinians in the Zeitoun and Sabra neighborhoods of Gaza City have left towards the north-western part of the city.
Gaza City residents described relentless bombardments overnight into Thursday.
“The house shakes with us all night long — the sound of explosions, artillery, warplanes, ambulances, and cries for help is killing us,” Ahmad al-Shanti told news agency AFP.
“The sound is getting closer, but where would we go?”
Amal Abdel-Aal was displaced from her home in Sabra a week ago and said she watched strikes hit the area.
“No one in Gaza has slept, not last night, not for a week. The artillery and air strikes in the east never stop. The sky flashes all night long,” she said.
An Israeli military spokesman said on Wednesday that troops were already operating in the Zeitoun and Jabalia areas to lay the groundwork for the offensive, which Defence Minister Israel Katz approved on Tuesday and which will be put to the security cabinet later this week.
Prime Minister Benjamin Netanyahu has said he is “shortening the timelines” for seizing what he described as “the last terror strongholds” in Gaza.
In a statement, Hamas accused the Israeli leader of continuing a “brutal war against innocent civilians in Gaza City” and criticised what it said was his “disregard” for a new ceasefire proposal from regional mediators. Israel has yet to formally respond to the plan.
About 60,000 Israeli reservists are being called up for the beginning of September to free up active-duty personnel for the operation.
Hundreds of thousands of Palestinians in Gaza City are expected to be ordered to evacuate and head to southern Gaza.
Many of Israel’s allies have condemned its plan, with French President Emmanuel Macron warning on Wednesday that it “can only lead to disaster for both peoples and risks plunging the entire region into a cycle of permanent war”.
The International Committee of the Red Cross (ICRC) meanwhile said further displacement and an intensification of hostilities “risk worsening an already catastrophic situation” for Gaza’s 2.1 million population.
Israel’s government had announced its intention to conquer the entire Gaza Strip after indirect talks with Hamas on a ceasefire and hostage release deal broke down last month.
