As the humanitarian crisis in Gaza continues to worsen by the day, Jens Laerke, spokesperson for the United Nations humanitarian office, said, "If there is a hell on earth today, its name is northern Gaza."

"People who remain there, the corners of their existence are death, deprivation, despair, displacement, and literally, darkness," Laerke said. "The entire Gaza Strip has been plunged into darkness. … What do you tell your children in such a situation? It's almost unimaginable."

People are fleeing Gaza's Al-Shifa hospital, sources confirmed to ABC News, in the wake of a strike on the exterior area of the hospital's outpatient clinic. One surgeon told ABC News "everyone" has fled, calling it a "nightmare."

The hospital has been treating thousands of wounded people and housing as many as 80,000 displaced residents, according to The Associated Press.

The hospital's head of plastic surgery, Dr. Ahmed Mokhallalati, told ABC News he is among the roughly 15% to 20% of staff members still there on Friday.

Although many patients have evacuated, he said, "There is no hospital in Gaza that can accommodate this number of ICU patients -- around 100 ICU patients."

The Palestinian Red Crescent said occupation snipers fired on Gaza's Al-Quds Hospital, killing at least one and injuring at least 28.

Israel Defense Forces spokesman Richard Hecht said, "The IDF does not shoot at hospitals. If there are Hamas terrorists in the hospitals, the IDF will do what it needs to, but we are aware of the sensitivity. We tell Hamas to move the sick southward."

"Slowly we are closing in on them and taking every precaution not to harm the innocent," he said.

American diplomats abroad are giving stark warnings about the long-term ramifications of the war, telling their Washington counterparts in multiple diplomatic cables that their work and public opinion of the U.S. in the Arab world could be lost and denigrated for a generation, a State Department source told ABC News.

Diplomatic cables are how U.S. embassies around the world privately communicate with State Department leadership about what U.S. diplomats are seeing on the ground. While some are just regular updates, others contain candid assessments and analysis about what senior embassy staff are seeing on the ground and the potential impacts on U.S. foreign policy or the U.S. standing in the region.

Twelve kids with cancer or other blood disorders have been evacuated with their families from Gaza to Egypt or Jordan so they can continue their treatment, the World Health Organization said.

More kids with cancer are expected to be evacuated, the agency said.

"I am relieved that children in vital need of cancer care have been able to leave the insecurity and uncertainty in Gaza and continue receiving life-saving treatment," WHO Director-General Dr. Tedros Adhanom Ghebreyesus said in a statement. "This show of desperately needed humanitarian action should serve to motivate increased access to life-saving care to all people affected by this conflict, both inside Gaza where needs are greatest today, and beyond. I pray this initiative can inspire all parties to put health and peace first."

The Israeli military on Monday accused Hamas militants of building "a whole tunnel system under" Sheikh Hamad Hospital in Gaza.

The practice of using hospitals as civilian shields has been "absolutely normal" for the militants, IDF spokesperson Jonathan Conricus said.

"Why it is this important? Because hospitals and other humanitarian facilities are supposed to enjoy special protections," Conricus said in a morning briefing. "But what Hamas is doing is that they've violating that special protection and using it for combat purposes."

More than 500 people have died in at least 102 strikes near or on health care facilities since Oct. 7, the World Health Organization said on Sunday.

"Over half of health attacks and over a half of hospitals damaged were in Gaza City," WHO officials said on social media. "Health care is #NotATarget."

During Monday's briefing, Conricus shared an IDF video that he said demonstrated there were Hamas tunnels under the hospital. He also shared several photos that he said dated back to at least 2010, when the hospital was being constructed. The groundwork for the Hamas tunnels was put in place at that time, he said. ABC News was not immediately able to verify the claims.

In a photo said to be from 2023, rocket-launching sites could be seen along the outskirts of the facility, Conricus said. He presented another photo of what he said was the opening of a Hamas tunnel on the grounds.

"We know that underneath this entire complex, there's an entire Hamas infrastructure underground," Conricus said. "And it is absolutely normal. This is how Hamas operates all around the Gaza Strip."

-ABC News' Kevin Shalvey