Hunter Valley police are appealing for anyone who was in the area of Old Maitland Road on Sunday or those who may have information to come forward after they were called to the area just after 5pm.

Investigators said they found the 54-year-old man injured before he was pronounced dead at the scene.

"As this is an unexplained death, it is currently being treated as suspicious," police said in a statement.

An investigation is underway and anyone with information is urged to call Crime Stoppers on 1800 333 000 or visit https://nsw.crimestoppers.com.au.