Police have launched an investigation into the incident, which occurred at Buchanan on Sunday night, and have appealed for anyone with information to come forward.

A NSW Roads and Maritime Services spokeswoman said yesterday the excavators were owned by a subcontractor doing drainage work in the Buchanan area, and would take several days to replace.

The fire is unlikely to delay construction work. The project team is expected to be back on schedule to conduct work at George Booth Drive and the Buchanan interchange on August 17.

“The project team is disappointed someone would deliberately vandalise equipment on the project,’’ the spokeswoman said.

‘‘Everyone involved on the Hunter Expressway is working very hard and it’s disheartening this vandalism has occurred.’’

The 40 kilometre expressway will be a four-lane divided road linking the F3 Freeway and Branxton.

Construction work on the project, which employs about 850 people, began in August 2010.

The Newcastle Herald reported recently that more than 85 per cent of the earthworks have been completed, and several bridges that form part of the eastern section could be opened next month.

The excavators were discovered alight at a section of the project, near Averys Lane, about 8.40pm on Sunday night.

Police and firefighters discovered two excavators ablaze, and a third already destroyed by fire.

The fire took several hours to extinguish safely, because diesel was fuelling the flames.

A number of heavy vehicles parked at the construction site were also damaged.