US investment bank Morgan Stanley Dean Witter & Co, which was the largest tenant in the World Trade Center, said in a statement it had "limited" information on the fate of its 3,500 employees there.
"Our key focus and concern are for the well-being and safety of Morgan Stanley employees," said chairman Mr Philip Purcell.
Morgan Stanley said in spite of the tragedy, all its businesses "are functioning and will continue to function".
"We are committed to resume full operations as exchanges and markets reopen. All our clients should rest assured that their assets are safe and our Financial Advisors will soon be in contact with our individual investors to answer questions and address their concerns," said Mr Purcell.
Merrill Lynch & Co Inc said it is asking all employees who work in the World Financial Centre and in other Merrill Lynch offices in lower Manhatten to stay home today.
Merrill said its offices throughout the rest of the US and the world will be open for business today, even though the New York Stock Exchange, Nasdaq and the American Stock Exchange will be closed.
"We want to assure our clients in and outside the US that their assets are safe and secure, and we will continue to provide a full range of services," the bank said in a statement.
Salomon Smith Barney, which leased a smaller office tower in the complex that also collapsed yesterday, confirmed that all its employees were successfully evacuated.
UBS Warburg issued a statement saying that none of its offices in New York have been affected by the attacks.
Credit Suisse Group spokesman Mr Paul Rimmer said the 800 Credit Suisse First Boston staff working in the World Trade Center Tower 5 were all evacuated in time in the wake of the terrorist attacks in New York, the Swiss daily Neue Zuercher Zeitungreported today.
Another Swiss bank UBS said none of its New York based operations were hit by the attacks.
AFP