On the morning of June 1, Dr. Victoria Rose was nearing the end of her 21-day stint as a volunteer in Gaza when she saw news of a mass shooting of Palestinians near a food distribution point.

A senior plastic surgeon in London, Dr. Rose, 53, had come to the enclave with a small British charity that has sent medical workers to humanitarian crises in countries including Bosnia and Herzegovina and Sri Lanka.

Dr. Rose went straight to the emergency room at Nasser Hospital where she was based, arriving around 8 a.m. It is the last major hospital still functioning in southern Gaza.

“There were ambulances coming in, just bringing dead people, and then there were donkey-drawn carts bringing dead people,” she recalled in an interview in London. “By about 10 o’clock, we had 20 or so dead bodies, and then easily a hundred or so gunshot wounds.”

In her three weeks at Nasser, Dr. Rose said she saw a health system under extreme pressure from an unrelenting stream of people with traumatic injuries. Compared with her previous two trips during the war, she said, many more patients have suffered “unsurvivable” burns or severe blast injuries from Israeli bombs.

“They weren’t shrapnel wounds anymore — bits of them had been blown off,” she said. “Children were coming in with knees missing and feet missing and hands missing.”