MUZAFFARABAD, Pakistan - Shopkeepers clashed with looters today, and hungry families huddled under tents while waiting for relief supplies after Pakistan's worst earthquake razed entire villages and buried roads in rubble. Death toll estimates ranged from 20,000 to 30,000.

British rescuers today unearthed a man trapped in rubble for 54 hours.

Eight U.S. military helicopters from Afghanistan arrived in Islamabad with provisions, and Washington pledged up to $50 million in relief and reconstruction aid, U.S. Ambassador Ryan Crocker said.

"The magnitude of this disaster is utterly overwhelming," Crocker said. "We have under way the beginning of a very major relief effort."

The United Nations said more than 2.5 million people were left homeless by Saturday's monster 7.6-magnitude quake, and doctors warned of an outbreak of disease unless more relief arrives soon.

With landslides blocking roads to many of the worst-hit areas, Pakistan's army was flying food, water and medicine into the disaster zone. International relief efforts cranked into action, and an American plane full of relief supplies landed at an air base near Pakistan's capital today.

Most of the dead were in Pakistan's mountainous north. India reported more than 800 deaths; Afghanistan reported four.

In the shattered streets of Muzaffarabad, where at least 11,000 people died, an Associated Press reporter saw shopkeepers scuffle with people trying to break into businesses. They beat each other with sticks and threw stones, and some people suffered head wounds. No police were nearby.

Residents of Muzaffarabad, the capital of Pakistan's portion of divided Kashmir, said looters also targeted deserted homes. Survivors lacked food and water, and there was little sign of any official coordination of relief in the devastated city of 600,000.

An eight-member team of British rescuers using a sniffer dog, drills, chain saws and crowbars pulled a 20-year-old tailor from the rubble this afternoon, 54 hours after a two-story building collapsed over him and dozens of others.

The man, Tariq, was wide-eyed and covered in dust when he emerged, and he begged for water.

"I haven't eaten in three days, but I'm not hungry," said Tariq, who suffered a leg injury and was carried away on a door serving as a stretcher. He had been trapped beneath concrete and wooden beams, and a dead body lay on both sides of him.

About 2,000 people huddled around campfires through the cold night on a soccer field on the city's university campus, where most buildings had collapsed and hundreds were feared buried in classrooms and dormitories. Soldiers burrowed into the concrete with shovels and iron bars.

"I don't think anybody is alive in this pile of rubble," rescue worker Uzair Khan said. "But we have not lost hope."

On the soccer field, Mohammed Ullah Khan, 50, said a few biscuits handed out by relief workers was all he had to eat for three days. His wife, who suffered a fractured leg, was wrapped in a yellow quilt beside him.

Their three-story home had collapsed in the quake. His family of 10 survived because they were on the top floor, which crashed to the ground. "My children are now on a hillside, under the open sky, with nothing to eat," he said.

A doctor, Iqbal Khan, said there was a serious risk of diseases such as diarrhea and pneumonia if drinking water and other relief supplies do not arrive quickly. "These people feel as if there is no one to take care of them," he said.

The city had no electricity, and people collected water from a mountain stream. Shops and the city's military hospital had collapsed.

Pakistani President Gen. Pervez Musharraf said the earthquake was the country's worst on record and appealed for urgent help, particularly cargo helicopters to reach remote areas.

President Bush on Sunday promised cash and said he had told Musharraf "we want to help in any way we can."

U.S. forces in Afghanistan prepared to send five Chinook transport helicopters and three Blackhawk helicopters to Pakistan today to help ferry relief supplies.

"Pakistan is one of our closest allies in the war on terror and we want to help them in this time of crisis," said Sgt. Marina Evans, a U.S. military spokeswoman in Kabul. "The terrorists make us out as the infidels, but this is not true, and we hope this mission will show that."