AMNA NAWAZ: Welcome to the "NewsHour."

Thirty thousand, that's the number of Gazans the Hamas-led Health Ministry there says have died in just 146 days of war.

That grim threshold was crossed after one of the deadliest single incidents of the war, more than 100 people reportedly killed trying desperately to pull aid from trucks.

GEOFF BENNETT: The need is dire and hunger acute.

The U.N. says more than half-a-million people in Gaza -- that's one out of every four - - are -- quote -- "one step away from famine."

The White House today called the deaths in Northern Gaza tragic and alarming.

And President Biden says it could complicate negotiations to pause the war and release Israeli hostages.

Nick Schifrin starts our coverage.

And a warning: The following report includes images that are disturbing.

NICK SCHIFRIN: They went to retrieve aid.

They returned instead with the dead and the food they desperately wanted for their families now covered in their blood.

It happened at 4:00 a.m., as Egyptian aid trucks arrived in Gaza City.

(GUNSHOTS) NICK SCHIFRIN: The sound of gunfire on this footage aired by Al-Jazeera as Gazans who'd come to gather aid began to flee.

And, afterward, residents walk away with bags of food surrounded by the injured.

Israel released this footage of crowds that surrounded the aid and what it called tanks securing the convoy.

That's when Gazans began fighting for food, said Israeli military spokesman Admiral Daniel Hagari.

REAR ADM. DANIEL HAGARI, Spokesperson, Israeli Defense Forces: The tanks that were there to secure the convoy seized the Gazans being trampled and cautiously tries to disperse the mob with a few warning shots.

When the hundreds became thousands and things got out of hand, the tank commander decided to retreat.

No IDF strike was conducted towards the aid convoy.

NICK SCHIFRIN: But at the Kamal Adwan Hospital, where the injured were rushed in, eyewitnesses blamed Israel.

MAN (through translator): We were surprised by Israeli tanks that came out and opened fire on people randomly and directly.

This is my brother, who went to bring food for his children.

If aid is to come to us in this way, we do not want it.

We do not want to live on the blood of our children.

NICK SCHIFRIN: But the aid is desperately needed.

The U.N. says, in Northern Gaza, one in six children under the age of 2 are acutely malnourished.

Some don't make it.

Doctors in Beit Lahia said this baby died of hunger and dehydration, a helpless mother left to grieve.

To a man with an empty stomach, food is God.

And for the Al-Awadeya family in Central Gaza, salvation comes from a plant that, like them, can survive the harshest conditions, a thorny, prickly cactus.

MARWAN AL-AWADEYA, Displaced Palestinian (through translator): Today, we are living in famine.

We have exhausted everything.

There is nothing left to eat.

We eat cactus, even with its thorns.

NICK SCHIFRIN: In Southern Gaza, volunteers from the international humanitarian organization MedGlobal document children's nutrition rates.

A UNICEF ruler shows an alarming truth.

The U.N. says famine in Gaza is looming.

DR. ZAHER SAHLOUL, President, MedGlobal: Hunger is a major issue right now.

And the severe malnutrition among children is alarming.

NICK SCHIFRIN: Dr. Zaher Sahloul is MedGlobal's president and co-founder.

He volunteered in several clinics and hospitals in Southern Gaza last month.

DR. ZAHER SAHLOUL: When we were there, there were no food, no chicken, no eggs, no milk, no fruits and vegetables.

Food were very expensive.

So average adult eats less than one meal a day.

NICK SCHIFRIN: Israel says there are no restrictions on aid and blames the limited flow of aid on the U.N. U.S. officials believe part of the problem is that Israel targets Hamas fighters who would be guarding the aid, leaving convoys vulnerable to the kind of incident that occurred today.

On Monday, Gazans flocked to the beach after Jordan airdropped aid into the sea, a drop into an ocean of need.

U.S. officials confirm they are actively planning for the possibility of U.S. airdrops.

DR. ZAHER SAHLOUL: This is something that has to be done because people are dying because of lack of food and lack of medicine.

And this should not happen in 21st century.

NICK SCHIFRIN: For the "PBS NewsHour," I'm Nick Schifrin.