The fire, which began at around 10.30am on Monday, is likely to cause problems with traffic diversions and irregular public transport throughout Tuesday, according to SL, the company which runs the capital city's public transport.
“It's still burning and we don't know yet how long we will need to be there. Probably the whole day,” said Hans Eriksson from the Stockholm fire service. “Now we are concentrating on protecting the other surrounding buildings.”
The fire began in connection with work on the roof of the building, which contains a large bus depot and the connected offices.
Eriksson said: “It's an old building with a roof built in a complicated way and construction work, so we haven't wanted to sent people up to the roof and fight the fire from within. That's another reason it's taken longer.”
No buses are reported damaged as most of the fleet were on Stockholm's roads at the time of the fire.
Police have opened an investigation into carelessness endangering of the public.