A British-trained orthopedic surgeon, Sohail Sahibzada, said he could not find his patient. A moment earlier, the young woman had been lying nearby on a gurney with a gaping infected wound on her broken leg. Now, she was missing. "We're in a bit of chaos at the moment," Sahibzada said during a pause in his search at the Ayub Medical Complex here. "The system is collapsing."

Following a strong aftershock Wednesday morning, several hundred earthquake victims had been shifted out of the hospital and onto the front lawn, some displaying bandaged stumps from amputated limbs. The operating theaters were no longer functioning because of fears that the building might collapse. New patients were still arriving at the rate of 40 to 50 per day, many with badly infected wounds.

"I don't know how long it can last," said Sahibzada, 51, reeling with fatigue after 12 consecutive days of performing and overseeing surgery at the hospital. "It's all just the beginning, not the end."

The chaos at the hospital underscored the monumental challenge facing medical and relief workers as they struggle to provide treatment for tens of thousands of people injured by the massive earthquake that rocked northeastern Pakistan on Oct. 8.

As in the case of many major earthquakes, this one exacted a gruesome toll in crushed limbs, smashed pelvises, broken spines, fractured skulls and other trauma caused by falling debris. But the injuries have been made worse in many cases by the difficulty of reaching survivors trapped in remote mountain villages. As time passes, medical workers say they are seeing more and more patients with gravely infected wounds.

"In principle, most of them are broken bones, but if they're open they're going to get infected very quickly," said Sebastian Nowak, who runs helicopter operations for the International Committee of the Red Cross in Pakistan. "They get black. They get gangrene. They get flies. They get worms. They get everything."

Because of the huge toll in injuries, and the difficulty of providing shelter in remote areas that will soon be blanketed by winter snows, relief experts said the earthquake in many ways poses a bigger humanitarian challenge than last year's Asian tsunami, even though it affected 11 countries and killed many more people. Estimates of the number killed by the earthquake range from 40,000 to 80,000, compared with more than 220,000 for the tsunami.

"The tsunami was something that you escaped completely or it killed you," said Kevin Hartigan, who runs the South Asia office of Baltimore-based Catholic Relief Services. "It was like a plane crash. Whereas the earthquake, on the contrary, was something that severely wounded many, many people in a very large, inaccessible area."

In Sri Lanka, the tsunami killed more than 30,000 people, traumatized many times that number and caused staggering property losses. But the damage was confined to a narrow strip of coastline, all of which was readily accessible by road, and most injuries consisted of relatively minor cuts and bruises. Medical teams that flew in to treat the wounded often found themselves with surprisingly little to do.

Nowak, the Red Cross worker, said he accompanied one young woman on a flight out of an isolated village on Sunday whose wounds were so badly infected, after three days trapped in the rubble of her house and several more waiting for treatment, that both her legs had to be amputated above the knee and her right arm above the elbow.

"About 20 percent of the patients I evacuate go straight to amputation," he said. Then he corrected himself: "It's more than 20 percent that get amputated. It's probably 30 percent. And I'm just seeing a small portion of it. There must be hundreds of villages like this."

The 7.6-magnitude temblor inflicted the bulk of its damage in the mountainous realm of Pakistani-controlled Kashmir and adjacent parts of North-West Frontier Province. With many roads blocked by landslides, thousands of injured victims have been carried down from the mountains by relatives or evacuated by helicopter. They are being treated at hospitals in Islamabad, the capital, and other cities, as well as a growing number of field hospitals.

One of the larger field hospitals is in the town of Mansehra, about 50 miles north of Islamabad, on the grounds of a government college, where classrooms have been converted into operating theaters and outdoor courtyards into recovery wards. The temporary facility is staffed and equipped by the private Shaikh Zayed Hospital in Lahore, about 150 miles southeast of the capital. On Wednesday, it provided care to about 150 patients, many of whom had been stranded without treatment for days.

"Still patients are coming with a lot of infections, with gangrene," said Arshad Pervez, a general surgeon who has performed three amputations since arriving at the temporary facility last week. "They tie their wounds with dirty clothes. Pus is pouring. Bones are infected."

About fifteen miles up the road to the north, on the edge of the devastated town of Balakot, the army of the United Arab Emirates has established a mobile field hospital equipped with air-conditioned operating rooms, 12 ambulances and a Bell 212 helicopter.

On Wednesday afternoon, the helicopter settled onto a makeshift landing pad in a cornfield next to the facility with a new patient, a 9-year-old boy from a mountain village more than 100 miles away. The boy's father, Qiyamat Gul, said the child had been injured in a landslide and had received only rudimentary care from a local physician. His right leg, crudely bound with blue cloth, was swollen to nearly twice its normal size and almost certainly was fractured, said doctors who examined him. Pus oozed from badly infected wounds on his foot, above his eye and behind his ear.

Nevertheless, said Azam Noor, a Pakistani surgeon, "I don't think there is any gangrene. If we manage it locally, it will get well."

The biggest medical facility in the area is the sprawling, three-story Ayub Medical Complex in Abbottabad, an old British hill station about 30 miles north of Islamabad. Sahibzada, the orthopedic surgeon, estimated that the hospital had treated more than 8,000 people since the quake and had performed more than 1,000 major operations, about 12 percent involving amputations. As for the young woman on the gurney whom he had lost, Sahibzada finally located her and arranged for her transfer to another hospital.

One of the patients recovering on the lawn Wednesday was Bagh Zareen, 13, who lay beneath a red blanket, somberly chewing a piece of orange-flavored gum that had been given to her by one of the doctors. Her left arm ended in a bloodstained bandage about four inches below the shoulder.

The girl had been fetching water from a spring, relatives said, when her arm was smashed by a boulder loosed by the earthquake. At the hospital, "We pleaded, 'Please don't cut off the arm,' " recalled the girl's uncle, Abdullah, who uses just one name. "They waited two or three hours and finally decided they had to do it."

The Ayub Medical Complex in Abbottabad, Pakistan, shifted victims to a makeshift hospital outside after an aftershock from the Oct. 8 temblor.