Central Station was thrown into chaos on Saturday night as a fire broke out in the Hungry Jack's restaurant in the main concourse of Sydney's main railway station.

Black smoke billowed out from the fast-food chain as alarms throughout the station went off at 6pm.

Fire crews attend fire at Central Station. Credit:Cole Bennetts

"You couldn't see anything; it was just black smoke covering the whole street," said witness Bradley Faragher.

More than 20 fire trucks had surrounded the station by 6.30pm as firefighters piled in to contain the blaze.