The physical architecture of the US financial system is understood to be mostly unharmed by yesterday's attacks. The New York Stock Exchange was undamaged and the American Stock Exchange computer systems and telephones were working yesterday. The exchanges and the banks have multiple systems designed to serve as back-ups in the event of catastrophes, including offices in Long Island and the other New York boroughs.

"The initial World Trade Center bombing sent a message to all firms on Wall Street that they needed to be prepared," a former bank chief said. "Every major financial institution in the world has serious redundancy plans." Until now these have never been pressed into action on a wide-scale basis.

Yesterday they were. A spokesman for Comdisco, which runs a disaster recovery business, said his firm had mobilised to provide office space, telephones and computers for 14 client firm, which have declared a "disaster". Mr Harvey Pitt, the SEC chairman, said trading would resume as soon as it was practicable to do so.