Israeli forces blew up homes and besieged schools and shelters for displaced people on Monday as they deepened their operations in Jabalia in the northern Gaza Strip, residents and medics said.
They also rounded up men and ordered women to leave the camp, they said.
Images on social media show dozens of men lined up.
Medics at the Indonesian Hospital told Reuters that Israeli troops stormed a school and detained the men before setting the facility ablaze. The fire reached the hospital generators and caused a power outage, they added.
Health officials said they refused orders by the Israeli army, which began a new incursion into the north of the Palestinian territory over two weeks ago, to evacuate the three hospitals in the area or leave the patients unattended.
Troops remained outside the hospital but did not enter, they said. Medics at a second hospital, Kamal Adwan, reported heavy Israeli fire near the hospital at night.
"The army is burning the schools next to the hospital, and no one can enter or leave the hospital," said one nurse at the Indonesian Hospital, who asked not to be named.
Palestinian health officials said 18 people had been killed in Jabalia and eight elsewhere in Gaza in Israeli strikes.
The Israeli military said troops were continuing ground operations across the Gaza Strip. It said in a statement that over the past day, troops had dismantled militant infrastructure and tunnel shafts and killed fighters in the Jabaliya area. It did not comment on the immediate situation regarding the hospitals and camps.
The UN Human Rights Office said it was "increasingly concerned that the manner in which the Israeli military is conducting hostilities in North Gaza, along with unlawful interference with humanitarian assistance and orders that are leading to forced displacement, may be causing the destruction of the Palestinian population in Gaza's northernmost governate through death and displacement".
Israel has intensified its campaigns both in Gaza and Lebanon days after the killing of Hamas leader Yahya Sinwar.
At least 87 people were killed after an Israeli attack on Saturday on northern Gaza's town of Beit Lahiya, the Palestinian enclave's health ministry said in a statement on Sunday.
Israel has vowed to eradicate Hamas, but in doing so has laid waste to much of the territory and killed tens of thousands of people. More than 1.9 million people have been left homeless amid a humanitarian crisis.
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