Anthony Barrett was in his room in the Sheraton Brussels Airport Hotel when a blast ripped through an airport terminal opposite.
Mr Barrett works for the Wales Audit Office and is in Belgium for a work conference.
He told ITV Cymru Wales: "I looked out of the window and I could see windows blown out of the terminal building, people fleeing from the building and at that point I saw at least one person lying on the ground."
Police forces across Wales are increasing their presence at key locations following the attacks in Brussels.
Wales' four forces will see more officers deployed at transport hubs.
The threat to the UK from international terrorism remains at severe as it has been since August 2014, meaning an attack is highly likely.
The public and businesses are being urged to be alert and report anything suspicious to the confidential Anti-Terrorist Hotline 0800 789 321.
Wales' First Minister Carwyn Jones says he is "appalled at today’s attacks in Brussels".
Cardiff Airport says it is "operating normally" following the explosions in Brussels this morning.
As Brussels Airport is currently closed passengers due to be travelling to Brussels from Cardiff via a connecting service should contact their airline for more information.
The Welsh First Minister Carwyn Jones has responded to the Brussels explosions, expressing his concern.