Lit by the ghostly glow of a rapidly depleting mobile phone light, Mahmoud Shalabi says conditions in northern Gaza have become "really dire" without adequate access to medicine, clean water, electricity or safe passage after nearly two weeks of Israeli bombardment.

"My wife is actually using her phone to light my face for this interview and [I am] using whatever charge is left in my phone, 45 percent, to conduct this interview with you," he told CNN's Erin Burnett in a video call.

For Shalabi, a local aid worker, a working phone is one of his most vital possessions.

But the drain on the battery was worth it, he said, if he could show people around the world what is happening in northern Gaza, the half of the enclave that Israel's military has told civilians to evacuate but where many nonetheless remain.

"With regards to the humanitarian situation right now, it's really dire," Shalabi, senior program manager of Medical Aid for Palestinians, stressed.

Gaza's 2.2 million people, half of whom are children, have been under sustained Israeli airstrikes since Hamas gunmen streamed out of the enclave on October 7 for an unprecedented murder and kidnapping rampage.

Some 1,400 people, mostly civilians, were killed in the worst single day massacre of Jews since the Holocaust. More than 200 people, including women, children and foreign nationals, were taken hostage by Hamas.

Israel's retaliation has been devastating for Gazans.

The Hamas-controlled Ministry of Health says more than 4,100 people have been killed, including hundreds of women and children -- even as Israel claims it is only targeting Hamas locations.

Israel has also cut off supplies of electricity, food, water and fuel to the Palestinian enclave in a siege that has been described by UN rights experts as "unspeakably cruel."

Northern Gaza, which contains the heavily populated Gaza City, has been hit especially hard and Israel's military has told civilians to evacuate south ahead of an expected ground offensive aimed at destroying Hamas and the many tunnels it controls under the enclave.

The shortage of food and power could "kill many, many people", a senior aid official warned on Friday, while UN Secretary General Antonio Guterres has called the evacuation of 1.1 million in northern Gaza "simply not possible."

Shalabi, a father of three, has been peppered with tough questions from his 9-year-old son about what their fate might hold.

"He asked me the other day and was crying, 'Dad, if I die, will I go to heaven or hell?'," Shalabi recalled. "I really couldn't answer. I choked for a few seconds and I said we will all go to heaven, my son."

Shalabi has decided to stay in the north, to continue trying to distribute what little aid his organization still has.

"We don't have electricity, we don't have fuel, we don't have water. You can't buy simple things for the kids, like you can't buy crisps or sweets, no fruits, no vegetables for the children," he said, adding that he had been queuing for two hours just to get 10 pieces of bread for his family, which also includes his parents.

"For the medicines as such, unfortunately it can't be done because there's nothing left in the local market," he said.

He added that the situation has been made worse by the lack of safe corridors and passages to warehouse stores.

"It's really difficult for us. We barely are working, but we are one of the very few organizations that are still functioning inside of the Gaza strip right now," he said.

The first trucks carrying humanitarian aid entered Gaza from Egypt on Saturday. The trucks entered through the Rafah crossing, the only entry point to Gaza not controlled by Israel, as seen by CNN's team on the Palestinian side of the border. The crossing closed quickly after 20 trucks went through.

Aid workers say they are a fraction of what's needed, with the World Health Organization saying Gaza requires 100 trucks a day to meet demands.

Hospitals across Gaza

Maintaining contact with hospitals has also been a challenge, Shalabi said, two days after a deadly blast at the Al-Ahli Baptist Hospital in Gaza City killed many civilians sheltering there.

The cause of the blast remains a point of contention, with Israel laying out what it said was evidence to show the explosion was caused by the militant group Islamic Jihad misfiring a rocket. Palestinian officials and several Arab leaders, meanwhile, have accused Israel of hitting the hospital amid its airstrikes.

The death toll cannot be independently verified, but the Ministry of Health in Gaza said more than 400 had died.

Scenes of chaos grip other hospitals across Gaza.

The UN Office for the Coordination of Humanitarian Affairs (OCHA) warned Friday that hospitals in Gaza are "on the brink of collapse," a situation made even worse because 60% of primary healthcare facilities have already shut down in Gaza.

The number of patients treated or waiting to be treated is at 150% of the hospitals' capacity, and people are lying on the floors and corridors, OCHA added.

A boy in a wheelchair with a head injury told CNN at a hospital how he had survived an explosion.

"We were playing in the garden and suddenly a missile landed on us," Mahmoud Al-Aloul said, adding that he was hit by a tree, while his grandfather, parents and brother were also injured.

Another boy, Abdurahman, 10, still does not know that the strike that injured him killed his mom, dad and three sisters. His aunt is the only one left to comfort him.

"I am worried about him, the shock when he wakes up and finds out that his mother and father are gone," she said.