The nation reeled in horror and security precautions spun into effect as the work day began with a series of plane crashes that left the World Trade Center in flames and smoke billowing from the Pentagon.

Americans far from the destruction sobbed, shook with anger or just stood, paralyzed by the unbelievable images on TV.

"I'm very afraid. I don't feel safe," said Charlin Sims, taking a cigarette break outside her office in downtown Columbus, Ohio. "I want to hug my son."

As the day wore on, the mood shifted from shock and fear to outrage and talk of retaliation. The attack drew angry words from the usually even-keeled Sen. Ben Nelson, D-Neb.

"We ought to serve notice to the terrorist world that you've had your last hurrah," Nelson said, speaking by telephone from a Washington location he would not disclose for security reasons. "We must spare no effort to find the responsible party, parties or groups and bring them to justice."

Bells at Trinity Episcopal Church in Columbus rang for the victims. Nationwide, crowds gathered around television sets in airports, bars, hotel lounges. The space station commander could see the smoke rising above New York.

"I'm devastated beyond belief. I mean, in many respects this is significantly worse than Pearl Harbor," said Lewis Eisenberg, chairman of the Port Authority of New York and New Jersey. A passenger stranded in Orlando also recalled the attack that brought America into World War II.

"We're like everyone else, in shock," said Carol Windham, a spokeswoman at Birmingham International Airport in Alabama. Planes were grounded nationwide.

Like many others who work in downtown areas nationwide, with large high-rises clustered close together, downtown Seattle workers were sent home even as they just arrived at their offices.

Lloyd Brian of Bothell, Wash., who works in the 24-story Westlake Center, was told the building was being closed at 9:30 a.m. PT.

"It seems a little surreal ... It was not so much as an option, they were telling us we had to leave," Brian said. "At first you think, why are they shutting us down, we're so far away? But then you think better to be safe."

Government offices from coast to coast launched emergency preparedness operations, even as questions were raised about how what appeared to be a well-coordinated terrorist attack could be carried out.

"It's sort of like a terrorism movie you see on television," said terrorism expert Michael Gunter at Tennessee Technological University in Cookeville.

The memory of Pearl Harbor was offered up again and again, with its images of sneak attacks, national honor and war.

"This is our second Pearl Harbor, right here in the nation's capital and New York City," a somber Sen. John W. Warner, R-Va., said as he stood in a capitol park after his office building was evacuated.

"Someone is trying to make a serious statement and I hope we do likewise," said Scott Gilmore at the Dallas-Fort Worth International Airport.

A World War II veteran in Nashville for a reunion of the USS Intrepid aircraft carrier crew was incensed.

"I feel like going to war again. No mercy," said Felix Novelli, a New Yorker with friends who work at the World Trade Center. "We have to come together like '41, go after them."

Planes were grounded nationwide, and heightened security went into effect at government and corporate offices including the Army's main germ warfare defense laboratory in Frederick, Md., city offices in Colorado and oil refineries in Louisiana.

Landmarks such as the Gateway Arch in St. Louis and the Space Needle in Seattle were closed.

"I don't think there's any place in America right now that's not at risk," said Andrew Hudson, a city spokesman in Denver, where emergency preparedness officials gathered in the basement of City Hall.

"It's just sick. It just shows how vulnerable we really are," said Keith Meyers, a computer technician watching police cordon off headquarters in downtown Columbus.

Others were angry, like Lynn Moore of Columbus. "I think they ought to start watching who we let into this country. We're just too generous," he said. "I think we've just become too comfortable."

In Philadelphia, dozens of people gathered in a hotel lounge to watch television coverage.

A visitor from Texas wept. "I can't believe what I'm seeing. I never thought I would see anything like this in my lifetime," said 20-year-old Beverly Evans of Dallas. "How can we stop something like this from happening?"

"I feel violated," said Lorna Cannon in Salt Lake City, where the sun shone, the buses ran on time, and everything seemed normal -- except for clots of people around television sets in the shopping mall.

Cannon feared for her son stationed at Sheppard Air Force Base in Texas. For all she knew, maybe that base would be next on the terrorists' list.

"You think of the Oklahoma City bombing as the worst thing possible, and then this happens," Cannon said. "I would just like to be with my husband right now. I would like to gather my family around me."

In Trenton, N.J., law-office worker Terry Rossi feared for her own life.

"I want to go home," she said. "I don't want to be in this building, the highest building in Trenton."

Students at Kansas State University in Manhattan skipped class to watch television, sometimes with professors' blessing.

"It seems ridiculous that I would stand in front of my class talking about Plato when something this important is going on," said Laurie Bagby, an associate professor of political science.

Jurors filing into a civil trial in Olympia, Wash., found an empty courtroom and a usually loquacious judge struggling for words. Superior Court Judge Daniel J. Berschauer stood before the jury without his black robe and announced that court would be canceled for the day.

"I wish I had something to say that would make sense of this for you," the judge offered.

In an Arkansas courtroom, a federal judge refused to halt a trial stemming from a 1999 American Airlines crash at Little Rock.

"We just can't stop," Judge Henry Woods said. "We have to go on."

ESPN.com senior editor Mike Grady contributed to this report.