"It was unreal. Spectacular. Like a movie," said a witness of the attacks on the World Trade Center. "Then, very scary."

Across America, disbelief gave way to fear.

One survivor was on the 64th floor of World Trade Center 2: "We actually saw the first plane crash into the other building and we ran towards the stairs to get out," he said. "We had reached the 15th floor of our building when it was hit. When we got out, we stood around in complete disbelief, surrounded by hundreds of tourists."

Down below, people looked up to see others jumping. "I saw about 10 of them from around the 80th floor. We couldn't believe what we were seeing. Some of them were in flames. Some of them weren't," said one woman, a block away.

Minutes later, there was a roar and the first building collapsed. It just peeled away and a billowing cloud of ash and dust and glass and steel began to crawl down Broadway, across Manhattan and into the eyes and throats of millions of New Yorkers.

Wall Street employees ran, a stampede in tears. "There were hundreds of emergency workers underneath, I don't know how they could have survived," said one. Nearby, people sought refuge in the subway, but the sandstorm of debris had reached there, too. Others grabbed for coffee-filters to act as makeshift masks. Some just stood and vomitted, lungs full of dust.

Uptown, New York was on a war footing. Priests were lined up on the streets. More than 50 hospitals were struggling to cope with the stream of injured. Emergency vehicles jammed the streets.

By mid-morning, downtown Boston was paralysed. The road to Logan Airport - where one of the planes originated - was eerily empty while downtown traffic was at a near standstill.

Workers flooded out of office buildings across the city as first the Prudential and John Hancock towers were closed, then federal buildings. By noon, most businesses had shut. The same story repeated itself in city after city, as America came to a sickened halt.

Some people seemed devastated by the tragedy, while others could not take it in. One woman shed silent tears while she clutched her baby outside her home in Beacon Hill, a smart residential neighbourhood in Boston. An ambulance administered oxygen to a man in the mid dle of a panic attack.

News of the attacks led to a speedy evacuation of Chicago's entire downtown business district, the Loop. By 9.30am, local time, thousands of office workers thronged the streets, most with cellphones glued to their ears and computer equipment in tow.

The Sears Tower, the tallest building in the US, was closed shortly after 9am. Across the road, the Chicago Mercantile Exchange (CME), one of the big futures markets, shut down its two trading floors.

Outside on the streets, traffic snarled, and minor rear-ending accidents developed. "I'm so sorry," wailed one woman driver, who had caused three cars to collide on West Monroe Street. "I just wanted to get home."

For all the frenzied activity, there was also a strange imperviousness, a resilience, a midwestern stoicism. Even as sirens wailed in the background, the city's farmer's market showed no signs of retreat. If anything, stallholders said, business was picking up as office workers grabbed bags of fruit for the journey home.

Californians braced themselves yesterday morning for their private portion of grief as they awaited details of the passenger lists of at least three missing aircraft.

Under silent skies, bereft of the usual buzz of commuter craft, helicopters and commercial jets, LA officials evacuated and closed landmark buildings such as City Hall and courthouses.

With all emergency services on full alert, Bernard Parks, police chief, chaired a crisis meeting in an underground emergency operations centre beneath police headquarters. All police leave was cancelled, and every available officer was ordered to remain on duty.

Like tens of millions of others, they left off what they were doing and gathered round televisions. They watched, wishing it were only TV.

Reporting by Prue Clarke, Lisa Fingeret, Tally Goldstein, Adrian Michaels and Stephanie Kirchgaessner in New York, Victoria Griffith in Boston, Nikki Tait and Christopher Bowe in Chicago, Tom Foremski and Louise Kehoe in San Francisco and Christopher Parkes in Los Angeles