Dr. Ahmed Yousef, an American pediatrician and director of an intensive care unit in Arkansas, embarked on a medical mission to Gaza, believing his expertise could help patients receive the advanced health care he was used to providing, The New York Times reported Saturday. But what he encountered far exceeded his worst expectations, forcing him to document the devastation, according to the newspaper.

“The first thing I did there was to triage mass casualties,” Dr. Youssef told the newspaper. “This was not advanced ICU care. Often we never got there, and patients died.”

According to the newspaper, Dr. Yousef volunteered with MedGlobal, a U.S.-based nonprofit that provides humanitarian relief around the world. After spending three weeks in one of Gaza’s last functioning hospitals, he described the devastating toll of the war on medical workers and civilians, especially children.

Dr. Yousef shared what he witnessed, including rare footage from inside Al-Aqsa Hospital in Deir al-Balah, with The New York Times.

During his stay in the hospital, medical teams worked tirelessly to manage the trauma victims who poured in as the Israeli army continued to bombard the surrounding areas, including humanitarian areas.

Staff were operating at three times the hospital’s capacity, often treating patients, many of them children, on pieces of cardboard on the floor. They also ran short of critical supplies, including blood, gauze and anesthesia. Many patients died from their injuries.

“I made the decisions again in high school, and we did the best we could,” Dr. Youssef said. “The longer I stayed there, the more I realized my role was not to be a doctor, but to be a witness.”

Dr. Youssef began sharing his daily reflections with his friends and family on WhatsApp. One entry from June 30 describes a teenage boy whose first words after his breathing tube was removed were: “Please let me call my dad. I just want to make sure he’s okay and he knows I’m okay.”

Officials in Gaza say at least 10,000 Palestinian children have been killed since the war began, with many facing lifelong physical and mental injuries. More than 500 health workers have been killed in the past nine months, according to international aid organizations.

Dr. Yousef’s comments reflect the increasingly grim reality of life in Gaza. On July 9, he wrote: “Every time I think things can’t get any worse, they do.”