PHOTOS: Vienna building collapse
Police spokeswoman Adina Mircioane says rescuers are trying to reach one injured person inside the residential building in Vienna's 15th district. Five other people are being treated for minor injuries.
Mircioane says other people may still be trapped inside the building, whose top two floors collapsed shortly after 10 a.m. Saturday (0800 GMT).
Austrian public broadcaster ORF a photo on its website showing a cloud of dust enveloping a street.