Zakar Hussain felt sick when he saw the school. Moments earlier, it had been a two-story stone-and-concrete building filled with hundreds of girls in blue-and-white uniforms. Now it was a heap of rubble, enveloped in a cloud of white dust. Already, he could hear the screams.

And somewhere inside was his daughter.

"Maria! Maria!" Hussain shouted, as hordes of other desperate parents converged on the scene. For nearly 30 minutes, he said, he frantically circled the flattened building, peering between broken concrete slabs with his weeping wife at his side.

Then, amid the cacophony of cries, Hussain heard a familiar voice. "Abu!" the 14-year-old girl shouted from somewhere beneath the wreckage. "Father!"

Strength and hope surging through his veins, the 50-year-old retired forester urged his daughter to stay calm, then grabbed a heavy stone and began pounding it against the concrete to make a hole.

So began one small, improvised rescue effort among thousands after the massive earthquake that rolled across part of South Asia on Saturday, killing at least 20,000 people, most of them in northern Pakistan, according to the latest official estimates. The 7.6-magnitude temblor, which officials described as the strongest on record in Pakistan, also caused damage and casualties in neighboring India and Afghanistan, but on a much smaller scale. Most of the destruction appeared to have been centered on or near Pakistan's side of the disputed Himalayan province of Kashmir.

With landslides blocking access to some stricken areas, and the government short of equipment and trained rescuers, Pakistan appealed for international financial and logistical support.

"Our helicopter resources are limited," Gen. Pervez Musharraf, Pakistan's president, told the BBC. "We need massive cargo helicopter support."

By Sunday afternoon, as in many stricken areas, residents of this normally bustling market town 100 miles or so north of the capital, Islamabad, still had not received any outside help. They estimated that as many as 150 students were still trapped in the wreckage of the school, but with no heavy equipment, they had all but given up the search. The only piece of rescue gear in evidence was a decrepit-looking bulldozer, donated by a private contractor. Its tread had fallen off before it could move any rubble.

In the town of Balakot, about 10 miles north of here, as many as 250 students were thought to be still trapped -- or, more likely, entombed -- in the wreckage of another school, news agencies reported. Villagers worked with sledgehammers and their bare hands to free the bodies.

The damage was said to be heaviest in Pakistani-controlled Kashmir, where the area's communications minister, Tariq Mohammed, told the Associated Press that "more than 30,000 people have died." That figure was considerably higher than other official estimates and could not be independently confirmed.

As the death toll mounted, international relief experts converged on Islamabad. The United States is sending eight helicopters and relief supplies, the State Department said. The United Nations and countries including Britain, Russia, China, Turkey, Japan and Germany have also offered assistance.

So did neighboring India, although that country did not escape unscathed, with reports of more than 500 dead near the cease-fire line that separates Indian and Pakistani forces in Kashmir. With many houses destroyed, families huddled under trees and plastic sheets, lighting wood fires against the mountain chill as they awaited help that by Sunday afternoon had yet to arrive in many areas.

The earthquake struck at 8:50 a.m. Saturday. Its epicenter was in Pakistani-controlled Kashmir 60 miles north of Islamabad, which escaped with relatively little damage, although dozens of people, and perhaps more, are thought to have died in the collapse of a 10-story apartment building.

During a drive Sunday from the capital toward the epicenter, the first signs of serious damage were visible about 116 miles north in Abbottabad, an old British hill station where a number of small apartment blocks and businesses -- including an ersatz "Best Western" lodging -- had been damaged or destroyed.

Things got worse in the Mansehra district, closer to the epicenter, where in places the road was buckled and nearly blocked by rockslides. Mud-brick homes exposed their contents through gaping holes. Some families had moved outdoors, setting up rope cots in empty fields, in apparent fear of aftershocks -- of which there have been many.

The earthquake wreaked havoc in Garhi Habibullah, situated in a fertile river valley dotted with cornfields and apricot orchards and surrounded by steep fir-covered hills. Many homes and stores had collapsed, spilling their contents into the streets. The body of a 10-year-old girl lay beneath a sheet on a rope cot awaiting burial.

Hussain, the retired forester, recalled the horror of Saturday morning.

A compact, sinewy man with a bushy beard and flat woolen cap, Hussain had risen before dawn with his wife and children to pray and eat a light meal before beginning a day-long fast in observance of the Muslim holy month of Ramadan. Carrying their book bags and wearing their school uniforms -- long blue tunic over white pants with white head scarf -- Maria, the 14-year-old, and her 15-year-old sister left home that morning at 7:30 in a buoyant mood, he said.

The sisters walked up the hill to the girls high school, where eight teachers taught about 750 students in classes as large as 100, residents said.

Hussain was in the courtyard of his home, reading verses from the Koran, when the ground lurched and the walls shook. The family reception room immediately fell in on itself. At about the same time, he said, "I heard a loud 'bang' " from up the hill in the direction of the school, about 100 yards away.

His wife and elderly mother were the first to grasp what had happened. "They shouted at me that the school had collapsed," he said.

Repeating a familiar Muslim invocation -- "There is no God but God and Muhammad is his prophet" -- the couple ran up the hill with Hussain's brother to a scene of utter horror. One of the school's five buildings, the one that housed Maria, had been flattened. Children beneath the rubble cried out for their parents, who frantically pulled at the wreckage with their bare hands. (Hussain's older daughter had been playing badminton outside and was not injured.)

After hearing his daughter's voice, "I felt I could move all this debris," said Hussain, whose bloodied and bandaged hands bore witness to his struggle. He and his brother pounded on the rubble for 15 minutes and finally opened a two-foot-wide hole. There on the other side, he said, was his daughter's tear-streaked face.

He grabbed her by the chin and pulled her, uninjured, to safety.

"I was very sure I would die," recalled Maria, a wavy-haired girl who says she wants to be a doctor. The teenager said she was sitting in Urdu class with 62 other children on the ground floor of the building when the earthquake struck. The teacher, Miss Yasib, had just begun the day's lesson, on "friendship and responsibility."

At the first jolt, many children ran for the exit, and some escaped outside, Maria recalled. But then the ceiling caved in, trapping her and several dozen other children in a dark space about two feet high. After she heard her father's voice, Maria said, she crawled about 30 feet through the gloom toward a pinprick of light, which grew steadily wider.

About 50 girls were pulled from the shattered building alive, according to Hussain and Mohammed Shafik, the school watchman.

Others met tragedy. By Saturday night, townspeople working with saws, shovels and sledgehammers had removed the bodies of 138 girls, including some from Maria's Urdu class, according to Hussain and other residents. Among the dead was Miss Yasib.

Villagers in Balakot, Pakistan, carry a survivor from a school that collapsed in Saturday's earthquake, which killed at least 20,000 people. An injured Pakistani baby is taken for an X-ray at an Islamabad hospital. Relief experts converged on the capital city.