The Red Cross warned on Saturday that any Israeli attempt to evacuate Gaza City would put residents at risk, as Israel's military tightened its siege on the area ahead of a planned offensive.
Gaza's civil defence agency said that since dawn Israeli attacks had killed 47 people in the territory already devastated by nearly 23 months of war.
Israel is under increasing pressure to end its offensive in Gaza where the great majority of the population has been displaced at least once and the United Nations has declared a famine.
But despite the calls at home and abroad for an end to the war, the Israeli army is readying itself for an operation to seize the Palestinian territory's largest city and relocate its inhabitants.
"It is impossible that a mass evacuation of Gaza City could ever be done in a way that is safe and dignified under the current conditions," International Committee of the Red Cross President Mirjana Spoljaric said in a statement.
The dire state of shelter, healthcare and nutrition in Gaza meant evacuation was "not only unfeasible but incomprehensible under the present circumstances".
The Israeli military has declared Gaza City a "dangerous combat zone", without the daily pauses in fighting that have allowed limited food deliveries elsewhere.
The military did not call for the population to leave immediately, but a day earlier COGAT, the Israeli defence ministry body that oversees civil affairs in the Palestinian territories, said it was making preparations "for moving the population southward for their protection".
Gaza's civil defence spokesman Mahmud Bassal told AFP 47 people had been killed in Israeli bombing since dawn.
The army did not immediately respond to a request for comment on the figure.
Media restrictions in Gaza and difficulties in accessing many areas mean AFP is unable to independently verify the tolls and details provided by the civil defence agency or the Israeli military.
Bassal said 12 people were killed when an Israeli air strike hit "a number of displaced people's tents" near a mosque in the al-Nasr area, west of Gaza City.
The army did not immediately respond to a request for comment.
Umm Imad Kaheel, who was nearby at the time, said children were among those killed in the strike, which had "shaken the earth" and filled the sky with smoke.
"People were screaming and panicking, everyone running, trying to save the injured and retrieve the martyrs lying on the ground," the 36-year-old said.
The civil defence agency said 10 people were killed by Israeli fire as they waited near food distribution centres in the central and southern Gaza Strip.
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