A 21-year-old man has been fatally stabbed in the chest at an Adelaide nightclub.

Police and ambulance offices were called to the Disco nightclub in Light Square just after 2.40am (Adelaide time) today.

Officers say they were responding to reports a man had been stabbed in the chest.

He was rushed to hospital but died on arrival.

Police say the man's family have been notified.

Officers are appealing for witnesses to the stabbing to come forward.