The 61-year-old was treated by paramedics on the ground, before being transferred to Westmead Hospital in Sydney by the Toll rescue helicopter.

Paramedics were told by work mates the man had lost consciousness for about five minutes after being injured by the falling timber but was conscious when paramedics arrived.

Police, and five units from NSW ambulance all responded to triple 000 calls to the incident which occurred at around 7.30am.

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Intensive care paramedic Adam Parker was among emergency personnel responding to the call, and said paramedics conducted a rapid trauma assessment of the patient, calling in the rescue chopper as part of their response.

Mr Parker said paramedics worked to stabilise the man at the scene; he was placed in an induced coma and intubated before being flown to Westmead Hospital in a critical condition, with trauma specialists at Westmead notified of his impending arrival.

The man was suffering a suspected fractured skull, and a large laceration, approximately 15-20cm to his head.

Inspector Gerard Powell, a duty officer with the Chifley Police District, confirmed police had also attended the scene, arriving at around 7.40am.

Airlifted to hospital by ambulance ...

As the incident occurred at a place of employment, Inspector Powell said police contacted SafeWork NSW, who will take charge of the investigation.

Police remained on scene until the rescue helicopter departed for Westmead at about 9.15am.

A spokesperson from SafeWork NSW said investigations were underway.

"SafeWork NSW is investigating after a truck driver was injured while loading a vehicle in Raglan. SafeWork inspectors have visited the site and our inquiries are ongoing."