The Hamas-run health ministry said those wounded in the strike could not receive care as doctors had been forced to evacuate the nearby Kamal Adwan Hospital.
At least 94 Palestinians were killed and dozens wounded in an Israeli strike on a residential building in the northern Gaza town of Beit Lahia on Tuesday, medical sources in Gaza said.
Marwan Al-Hams, an official at the health ministry, said 150 people were wounded. Medics said 20 children were among the dead.
There was no immediate Israeli comment. The IDF has frequently questioned figures on the death toll published by the Hamas media office, saying they were often exaggerated.
Video footage obtained by Reuters showed several bodies wrapped in blankets on the ground outside a bombed four-story building. More bodies and survivors were being retrieved from under the wreckage as neighbors rushed to help with rescue.
"There are tens of martyrs [dead] – tens of displaced people were living in this house. The house was bombed without prior warning. As you can see, martyrs are here and there, with body parts hanging on the walls," Ismail Ouaida, a witness who was helping to recover bodies, said in the video.
On Monday, the Palestinian Civil Emergency Service said around 100,000 people were marooned in Jabalya, Beit Lahia and Beit Hanoun without medical or food supplies. Reuters could not verify the number independently.
The health ministry said on Tuesday those wounded in the strike could not receive care as doctors had been forced to evacuate the nearby Kamal Adwan Hospital.
"Critical cases without intervention will succumb to their destiny and die," the ministry said in a statement.
Gaza's emergency service said its operations had come to a halt because of the three-week Israeli assault into northern Gaza. Israel says its campaign is to destroy Palestinian militant group Hamas, whose fighters had returned to the area in the year-long war.