The fire that ripped through a 26-storey building in Bathurst Street in Sydney's CBD has now been extinguished, authorities have confirmed.

The fire, which is believed to have been caused by an electrical fault, caused major traffic delays throughout the day as several roads were closed. Two eastbound lanes on Bathurst Street remain closed.

At 5pm the fire was completely extinguished. However, four fire crews have remained at the scene ventilating the building, Fire and Rescue NSW, Ian Krimmer said.

Peak hour commuters faced heavy traffic when leaving the city tonight, a spokeswoman from the Traffic Management Centre said.