Mass grave is being dug at the Al-Shifa hospital in Gaza City, a witness tells a BBC reporter in Gaza.
The witness says he saw 30 bodies buried there – a doctor at the hospital says the total is 200 bodies.
Fighting between Israel and Hamas is raging in Gaza City, including at the hospital site.
Israel has accused Hamas of running a command centre under Al-Shifa – which the hospital and Hamas deny.
The hospital’s lack of fuel means premature babies and dialysis patients can’t get treatment, the UN warned earlier.
Meanwhile, Israel has confirmed the death of 19-year-old Noa Marciano, a soldier who was kidnapped by Hamas last month.
Israel began striking Gaza after the Hamas attacks on 7 October, in which 1,200 people were killed and more than 200 taken hostage.
The Hamas-run health ministry says more than 11,000 people have been killed in Gaza since – of whom more than 4,500 were children.
