The attack on the World Trade Center, one of the greatest symbols of U.S. capitalism, destroyed the offices of some of the most famous names in American and international commerce and left their out-of-city colleagues fearing a big death toll.

The twin towers, whose floors covered almost the same amount of space as all of the office buildings in downtown Toronto, contained the offices of Morgan Stanley Dean Witter Co., one of the world's largest investment firms, Switzerland's Credit Suisse Group, Germany's Commerzbank and Thomson Financial, whose parent company, Thomson Corp., is based in Canada.

Cantor Fitzgerald International, a London-based bond broker, occupied several upper floors of the North Tower.

No figure of the number of dead in the buildings was available last night, although Roman Catholic priest Roger Fawcett, a spokesman for Saint Vincent's Medical Center, said there were "hundreds, maybe by the thousands of victims" from the collapse of the first tower. As many as 50,000 people worked in the towers. New York Mayor Rudolph Giuliani said about 10,000 were there at the time of the attack.

Morgan Stanley was by far the largest tenant, with 50 floors and about 3,500 employees. At midafternoon, the firm distributed a memo to employees saying that World Trade Center personnel had survived the attack and that senior management were in the company's midtown offices at the time of the assault.

Later, it put out a new statement, saying the company had yet to determine how many people it may have lost. The firm also doesn't know how many of its employees left the building before it collapsed.

Morgan Stanley employees said they expected to hear of injuries or deaths.

"It would be an absolute miracle if no one was killed because most of the Morgan people would be in their offices by 9 a.m.," said Nathaniel Foster, 25, a Morgan Stanley trader in the company's London office. "The impact to us could be quite devastating."

About 200 Thomson Financial employees worked in the World Trade Center, although the company said it did not know how many were there at the time. One Thomson employee had a reservation on a hijacked airplane, said Dick Harrington, Thomson's chief executive officer.

Several other Canadian companies had offices in the towers, including the Toronto-Dominion Bank and the Bank of Nova Scotia. The banks said all the employees were accounted for. The Bank of Montreal's chief economist, Paul O'Neill, was due to attend a conference in the Trade Center and was either in or near the building at the time the planes hit, a bank spokesman said. He escaped injury.

There were more details about the victims of the four hijacked planes, carrying a total of 266 people. Among the more senior business people aboard was Phil Rosenzweig, a software-engineering director at Sun Microsystems, one of the world's largest makers of computer servers. He died aboard American Airlines Flight 11, one of the two Boeing aircraft that crashed into the towers.

David Angell, 54, executive producer of the NBC television show Frasier, was also aboard Flight 11 with his wife Lynn, according to Mr. Angell's brother. They were returning from their summer home in Chatham, Mass., where they had attended a wedding weekend.

Barbara Olson, a CNN commentator and the wife of U.S. Solicitor-General Ted Olson, was one of the 64 people who died on the jetliner that crashed into the Pentagon.

Ms. Olson made two cellphone calls to inform her husband that the airplane had been hijacked.

Sun Microsystems had 300 employees in the buildings, of whom 200 were present. All escaped because they were on the 25th and 26th floors of the 110-floor structures. A mid-sized company, an Internet content distributor called Akamai Technologies Inc., said one of its co-founders was killed when the jet he had boarded crashed into the centre. He was Daniel C. Lewin, who also served as the company's chief technology officer.

A spokeswoman for insurance-broker Marsh & McLennan said only 500 of its 1,700 workers in the World Trade Center were accounted for.