he city changed forever yesterday. No one, no matter how far from Lower Manhattan, could step on a New York sidewalk untouched by concussions.

The day began in the brilliance of a late summer morning, then was obscured in gray balls of dust and smoke that seemed to touch everyone. The city had become an empire of the stricken.

Erin Dubin, 26 and an aspiring Broadway dancer from Minnesota, had started the day with an audition for "Footloose," hoping for her big break. At midmorning, tears rolling down her face and a cell phone dangling from her limp hand, she stood stock still on 43rd Street at Seventh Avenue, staring but barely taking in the news ticker across the street. Her boyfriend worked at Lehman Brothers in the World Trade Center as a Web page designer.

Normally he arrived at work at 9 a.m. and Ms. Dubin fervently hoped he had been delayed. But she could not reach him.

"I hope he was late," she said, frozen in place as the words scrolled endlessly across the buildings at Times Square. "I don't know exactly what I should be doing. Where should I go?"

New Yorkers were members of a tribe in shock, tied in knots and easily moved to sudden tears and swift kindnesses. People moved through Midtown without the ordinary get- out-of-my way pace. They listened to radios. They grabbed one- minute updates from strangers. They spoke urgently into cell phones. They waited quietly in long lines — no shoving, no impatient words — at the pay phones on street corners. The hundreds who sat or stood under outdoor jumbo electronic television screens were virtually silent; it was no time for small talk.

Further uptown on Eighth Avenue, a crowd stood around a delivery van, listening to radio reports.

By midmorning, when the news had filtered out to just about everybody and the great cloud of black smoke at the southern end of Manhattan had become a permanent blot on the horizon, businesses began to close down and bars began to fill up. Smokers who had quit decided to take it up again, at least for the day. A bus would stop, going uptown, and people rushed to get on, no matter what its destination.

"Will someone ask the driver where this bus is going?" shouted a woman as she propelled herself toward an M2 limited bus on Madison Avenue. "Just get on or you'll never get out of Manhattan," called back a teenager near the front.

But getting places was out of the question for most people. The only way to go was north, or east, away from the fires and destruction. And for most, the only way to go was on foot. They found bridges closed and highways open to pedestrians and subways stopped dead.

Jim Speziale, driving a bread delivery truck, took pity. He stopped his truck on Park Avenue at 33rd Street, opened the door and invited people in. "I'm going up as far as 59th Street," he shouted to the crowds on the sidewalks. They climbed in by the dozens.

People who made it across the Manhattan Bridge were met by workers from Long Island College Hospital and Brooklyn Hospital Center. They were handing out water and fruit juice to those beginning to trudge down Flatbush Avenue.

"Water and medical attention here!" shouted Claudine Rose, normally a clerical worker at the Brooklyn Hospital Center. "You can call your families across the street and let people know that you're okay."

It was almost as if the city had turned tender, as if people wanted to tip-toe around each other so as not to cause any upset. Normal reactions — irritation at stalled traffic, peevishness at pedestrians who stopped in the middle of the sidewalk — were muted.

There were refugees everywhere: a long, slow motion flight from the core of the city, great strings of people putting their feet on the ground, in hopes that it, unlike the sky, was safe. And because they would be putting down their feet many times, some women stopped on Canal Street to buy $8 flip-flops, a small advantage over high-heeled shoes for such a journey.

As those brushed by the attacks drifted away from the neighborhood around ground zero, they were met with acts of grace, large and small. Keith Vance reported that he found himself a few blocks away from the collapse, in front of a Chinese delicatessen. The proprietor came out with bottles of water. Then a man in a hardware store handed out dust masks used by plasterers.

The numbers of walkers grew as the devastating news took hold. Maria Thomas, at work in Macy's when she heard about the explosions, decided not to stay. "Look, Macy's is a landmark building, you know," she explained from 10 blocks away. As she left, customers were streaming into the store, apparently unaware of what was happening in Lower Manhattan. "It's believable and at the same time it's not believable," said Ms. Thomas.

That was the mental line many people walked: how could this horror, which would not be credible on a movie screen, be actual, be real, be flesh and blood?

For some of those who had been downtown, the horror of the moment emerged as they walked miles toward home, carried along on waves of shock and contemplation. Ed Lamm, who works at J.P. Morgan in New York Plaza, said he could not escape the image.

"It's devastating, just looking back at that scene," said Mr. Lamm, 53, of Mineola, as he crossed the Manhattan Bridge. "The smoke, the darkness. It's like the day stood still.

"You're aware what's in the sky, checking for planes, seeing F-15's in the sky. But we're the lucky ones, we're alive."

Carole Kitrosser, a financial planner who normally works a few blocks from the World Trade Center, was seeing clients uptown yesterday. Her country would never feel the same. "If they can stop New York City from functioning, what happens next?" Ms. Kitrosser said.

"But I felt violated, that my safety was violated and that this country has got to do something to protect us," Ms. Kitrosser said. "I don't think I can ever go downtown to work again. I don't think I can look at the rubble. Our schools are closed. Our financial district is closed. We're not safe anywhere."

For those at a distance, the pace of events — one crash, a second crash, a collapse and then another — brought a slow-motion fear, rising like a tide into consciousness. In Brooklyn Heights, Lisa Morris heard a radio report about the first plane crashing into the tower, and walked onto the street to look across the harbor.

"The first building was in flames and the second plane came right across and went into the second building," she said. "It must have flown over the Statue of Liberty and come right in.

"It was strange to think that the first crash was a horrible accident. And the second, knowing it wasn't an accident, made it so much worse," Ms. Morris said.

Moved by the television and radio coverage, lines of volunteers turned up at hospitals across the city, prepared to donate blood for the survivors. Many were turned away because the hospitals were not ready to accept them, or actually found themselves with enough on hand — and too few survivors in need of it.

In the Gristede's at Broadway and 108th Street, David McCarthy, 40, was one of many buying jugs of water, "just in case." He added: "I went to the bank, and all the banks except one were closed. And I realized, wait a minute, something's going to happen."

As hard to absorb as adults found the day's events, their worries for children were of another order of magnitude.

"What am I going to tell my daughter?" said Carmen Diaz, who was sent home from her Midtown office along with other employees and was wandering around, hugging a transistor radio, until her daughter's school let out at 3 p.m. "I don't even know myself why such a thing could happen. It will be so hard to explain."

Within an hour of the disaster, hundreds of anxious parents had massed at Public School 192, a school that serves many Dominican immigrants in West Harlem. Some feared a world war would break out, and wanted to protect their children. Others said that if the World Trade Center had been destroyed, then why shouldn't a school be next? Most said that when they heard the news they simply wanted their children to be with them. By 11:40 a.m., parents had picked up all but 150 of the 1,700 students in the school.

Elton Callender, who came to get his nephew, a first grader, said he did not want the boy to hear the news from a stranger and panic. "I just need to explain this stuff to him," Mr. Callender said. "Actually, I'm scared that there could be a world war."

As another boy and his father walked home, tightly holding hands, the boy said: "Papi, did you notice that some people blew up a house?" His father corrected him. "Blew up the World Trade Center."

"Wha?" the boy exclaimed. "I thought it was a house. And some people died, right?"

"Right," his father said tersely, and kept walking.

Many sought solace in prayers, either alone or in the great holy spaces of the city. Tom Brown, a street corner preacher on Broadway and Canal, had handed out about 500 tracts in 90 minutes. "People think this stuff is baloney, but today they're listening," Mr. Brown said.

At 9 a.m. a bell at the Cathedral Church of St. John the Divine began tolling in the slow, steady rhythm of mourning. In the evening, Cardinal Edward M. Egan said Mass at St. Patrick's Cathedral, praising the efforts of rescue workers and those providing medical care. "I saw New York at its best," he said. "I saw police officers and firefighters careless of their own safety, interested in only serving this great city, covered in soot. I saw many of them bleeding from the necks and arms. They're New York at its best. They inspired this New Yorker with pride."

The cardinal said that he had administered last rites to 12 to 15 of the injured who were taken to St. Vincent's Manhattan Hospital. He said one of them died about six minutes later. At one point while he was at St. Vincent's, he looked up and saw the second tower collapse. "It was a nightmare, a nightmare for this city of noble and decent people."

Places of worship all over the city propped open their doors, offering everything from pasta and coffee to a spiritual perspective. And what might normally be seen as unwelcome proselytizing was embraced. At the Middle Collegiate Church on Second Avenue in the East Village, a congregant stood on the steps, urging anyone who paused to come on in. Many took him up on it: people covered in soot, a man who had watched his co-worker die, a woman who worked on the 19th floor of one of the towers and could not reach her daughter.

"There's nothing but death in the air today," said Debbi Gibson, a paralegal who lives in East Harlem. "I don't want to hate anybody. I don't want to judge anybody. So in order to keep my peace I had to be here for a little bit."

Even those who offered solace were not untouched by the tragedy. In the basement of St. Joseph's Church in Greenwich Village, Veronica Johnson, a parishioner, busied herself over a counter laden with food meant for rescue workers, pulling her sunglasses on as she struggled with news that the body of a familiar friend, the Rev. Michael Judge, had been identified. Father Judge was a Fire Department chaplain. "He married my son. He baptized the kids. He's been there for everybody," she said, her face suddenly damp.