Five of Regus' staff at its serviced office centre in the World Trade Center in New York were killed in yesterday's terrorist attack.
Chief executive Mark Dixon is now on his way to the US.
In an official statement, Dixon said: "It was confirmed overnight that five members of our staff are unaccounted for. We are devastated by this tragic news and our thoughts are with the five individuals, their family and friends. The situation for our clients is unclear, and yet to be confirmed", said Dixon.
The centre, opened this spring,
occupied the 93rd floor of Tower 2.