Police said the 76-year-old man was trapped under an all-terrain side-by-side vehicle when it flipped on the farm about 5pm.

Chifley Police District duty officer Inspector David Abercrombie said emergency services were quickly called to the property but the man could not be revived and died at the scene.

"The accident occurred about 5pm on a property at Oberon when a 76-year-old gentleman was conducting farmwork on his property utilising a side-by-side all-terrain vehicle," Inspector Abercrombie said.

"Whilst conducting his farmwork the buggy has flipped and the man was trapped underneath.

"Tragically, he received fatal injuries as a result.

"Police and all emergency services attended, including a helicopter, but the man could not be saved."

Inspector Abercrombie said Chifley detectives were called to the scene late yesterday and have started an investigation into the cause of the crash.

A report will be prepared for the coroner.