The true measure of tragedy has started to emerge. On the third day, with smoke still pouring out of the debris and filling the lower Manhattan sky, accurate numbers of those missing started to be posted.

Rudolph Giuliani, New York's mayor, said that 4,763 people were unaccounted for at the World Trade Center. That could be 10 per cent of the twin towers' daytime population. It had been assessed from the diligent and frantic work of 400 despairing businesses that worked in the buildings, the aircraft passenger lists and the emergency services.

By Thursday, complete lists were readied. Keefe, Bruyette, & Woods, a broker with 171 staff, posted all their names on its website. Beside each one was either "Safety Confirmed" or "Unconfirmed". The missing 67 were probably near the top of Two World Trade Center. About 15 people from Morgan Stanley were missing. "What dominates our concerns are those people who may not have escaped the explosion and fires as the twin towers collapsed," said Philip Purcell, chairman of the investment bank.

However, there was relief for many too. Morgan Stanley was by far the biggest tenant of the WTC, with 3,700 people on over 20 floors. Almost all of those have now been contacted.

But elsewhere the news was stark. Cantor Fitzgerald's employees were on almost the very top floors of the north tower, the first to be hit on Tuesday. Three staff members on a lower floor survived. But of about 800 in Cantor's main offices, not one has been seen alive. About 300 other Cantor employees were out of the office that day.

Howard Lutnick, Cantor's chief executive, was at times too distraught to talk when he gave an interview to ABC television: "My little boy. . . it was his first day of kindergarten. . . I took him for the first day of big-boy school." Mr Lutnick was not in the office on Tuesday morning.

Recovery of bodies has been painfully slow. Aside from the enormity of digging through 220 stories of the collapsed towers and other buildings, the disaster area is still being repeatedly evacuated as nearby structures become unstable.

Over 11,000 body bags have been ordered but only 94 bodies had been taken out by Thursday afternoon. There were also 70 body parts, a horrific reminder that exploding aircraft fuel, prolonged fires and disintegrating masonry were unlikely to leave many bodies identifiable or intact.

The situation was "horrible and gruesome" Mr Giuliani said. "I'm sorry that I have to describe it that way, but that's unfortunately the situation that we're facing."

Of some of the other large tenants, the Port Authority was missing 200 of its 1,500 staff. Marsh & McLennan and Aon, the world's two largest insurance brokers, had 2,800 staff in the WTC. Some 600 from Marsh were missing.

Bank of America said eight employees had not been contacted out of more than 400. Japan's Fuji Bank said 12 of its 125 Japanese employees were missing, together with roughly 50 of its 500 non-Japanese staff.