The cause of the collapse and the exact nature of the work being carried out at the site are not yet clear, said a police spokesperson. The building is old, typical of the area, with most dating back to the 19th century.

An ambulance service representative said that another person, a 45-year-old man, has been seriously injured.

The street where the accident occurred, Porzellangasse, runs through the heart of the aristocratic district, near the French School and the nearby Liechtenstein Palace, one of the city’s most luxurious historic palaces.

The police are taking statements from eyewitnesses and workers who survived the accident, the spokesperson added.