Paving stones flew into the air and one woman is reported to have been knocked out of her chair at a nearby cafe by the powerful explosion.
"Two people pulled the lady up and then ran off,” a witness told the Kronen Zeitung newspaper.
A short while later police arrived and ordered that the designer shop on Wallnerstrasse be evacuated. Employees and customers took refuge in nearby Michaelerplatz.
A large part of the Wallnerstrasse had to be cordoned off, and surrounding shops were closed.