The accident occurred around 1.45pm, when a sewerage trench in which the men were working collapsed.

The trench was about 60 metres long and five metres deep.

One man, aged 44, was trapped for a short period of time before being freed by nearby colleagues.

He was treated at the scene by paramedics and taken by road ambulance to Orange Base Hospital, suffering lacerations and undisclosed chest injuries.

The other man, who was buried from the shoulders down, remained trapped for more than three hours while emergency crews dug him out by hand. 

It was deemed too risky to bring machinery in, as any vibration may have caused a further collapse.

Two doctors, paramedics, NSW Rural Fire Service and State Emergency Service, as well as police and Police Rescue, remained on the site working to free the man, who was released just before 5pm.

After being treated at the scene, the man was transferred by air ambulance to Orange Base Hospital, suffering a suspected dislocated shoulder and grazing to his legs. 

Yesterday the work site was deserted, having been fenced off and the trench filled in.

A WorkCover NSW spokesperson confirmed investigators had attended the accident site on Thursday afternoon, and had started an investigation.

The spokesperson made no other comment, other than to say the investigation was in its infancy.