Hundreds of people had to be evacuated from the building in Pelikanstrasse after the fire was reported just after 10am on Thursday morning, Zurich rescue services said in a statement.
A total of 25 people received medical attention on the scene, but no one was hospitalised.
#Grosseinsatz der #Feuerwehr wegen #Dachstockbrand im Kreis 1. Die Liegenschaft sowie die angrenzende Baustelle wurden komplett evakuiert. Verletzte sind keine zu beklagen. Die Lösch- und Aufräumarbeiten sind sehr aufwändig. Zur Medienmitteilung: https://t.co/xcjcldTPV4 ^sc pic.twitter.com/2aPZCCUuSp— Schutz & Rettung ZH (@SchutzRettungZH) April 26, 2018
The fire was finally extinguished after six hours.
The operation was described as "complex". Firefighters needed to cut holes in the copper sheet roof to get at the burning wooden layer below.
There are construction works going on near the UBS building and cantonal and city police are now investigating if these may have played a part in the fire, rescue services said in their statement.