A man has died after a house was engulfed by flames in Sydney's Upper North Shore on Monday night. 

Emergency services were called to a house on Blackburn St, St Ives after reports of a fire just before 7pm, where they found the home "engulfed in smoke and flames", according to police. 

It took an hour for the fire to be extinguished. 

When firefighters conducted a search of the property, they located the body of a man, who they believed was the 81-year-old occupant of the house.

Police have established a crime scene and will investigate the fire.

Anyone with further information should contact Crime Stoppers on 1800 333 000.