Fire crews fight Sydney building blaze

Fire crews have raced to the scene of a building fire at the edge of Sydney's CBD.

The fire broke out on a rooftop in Haymarket around 5.15pm on Monday.

Northbound roads into the George Street building are closed as emergency crews work to extinguish the blaze.

It's believed the blaze started in the kitchen of a restaurant in Capital Square.

An oil vat caught fire and the flames then shot up an exhaust duct, causing smoke to billow out.

Those in the George Street area are advised to 'exercise caution'. Source: Twitter

Around 100 people were evacuated from the scene.

Motorists are being diverted on to Pitt Street, while people in the area are advised to exercise caution.