"The 30-year-old victim suffered stomach and back wounds, but is not in danger," police spokesman Paul Eidenberger said.
The suspect, a 40-year-old former employee, barricaded himself in the building after stabbing the porter and was arrested by armed police.
He had tried to enter the building in Vienna’s 9th district around 6am on Tuesday but the night porter had refused to let him in as he had been banned from the agency.
He pulled out a kitchen knife and stabbed the porter. The victim was treated on the spot by staff from the nearby AKH hospital.
Eidenberger said the suspect appeared to be mentally distressed when he was arrested.