Scores of people including hospital patients fled Gaza City’s main hospital on Saturday to avoid being struck by Israel missiles.
They said they were warned to leave by some hospital staffers in Gaza.
Many were seen walking along rubble-strewn streets as gunfire rang out.
Separately Hamas health officials said two explosions in Jabalia in northern Gaza together killed 80 people.
It was gathered that there are footage of women and children – with severe injuries or lying motionless on the floor in different parts of al-Fakhoura school building.
There are more than 20 such casualties visible in the footage, and around half of these are seen in one particular room on the ground floor, which also shows signs of considerable damage.
The head of the United Nations agency for Palestinian refugees (UNRWA) Philippe Lazzarini said he had seen “horrifying images and footage of scores of people killed and injured” in one of his agency’s schools “sheltering thousands of displaced”.
“These attacks cannot become commonplace, they must stop,” he said.
Separately, the Hamas-run health ministry said more than 30 people from the same family had been killed elsewhere in Jabalia, in what it also said was an Israeli strike.
The Israel Defense Forces (IDF) had no immediate comment on the report but said it was expanding operations in Gaza, including in Jabalia, to target Hamas.
The Hamas-run health ministry says the death toll in Gaza has reached 12,300. More than 2,000 more are feared to be buried under rubble.
