Lebanese national Albert Metledge was found dead on Wednesday and his son Antony was left in a critical condition after a man attacked the two at their inner-Sydney construction site, as reported by abc news.

Paramedics found the 76 year-old property developer at a construction site he owned on Applebee Street, in St Peters while his 33-year-old son is now in a stable condition after undergoing surgery at the Royal Prince Alfred Hospital.

Emergency services indicated that the assailant is a 49-year-old man who stabbed the pair then fled the scene.

NSW Police have launched a massive manhunt for the suspect who was described as being Caucasian, with a large build and a shaved head.

Police revealed that the men involved were known to each other and it was not a "random attack.”

The father and son were well respected within Sydney's Lebanese community.