The World Health Organization (WHO) has described al-Shifa hospital in Gaza City as a "death zone" after a visit to the site.
A joint UN team led by the WHO assessed the hospital for one hour following its occupation and evacuation by the Israeli military.
The team said they saw evidence of shelling and gunfire and observed a mass grave.
Following an evacuation which the hospital director said was ordered by the Israeli army but which the army said was requested by the director, 300 critically ill patients remain in al-Shifa.
The WHO said it was trying to arrange the urgent evacuation of remaining patients and staff to other facilities in Gaza, and repeated calls for a ceasefire.