A young motorcyclist was airlifted to hospital in a critical condition after crashing into a tree in the lower Blue Mountains this afternoon.

The CareFlight rapid response trauma team were called to Single Ridge Road, Yellow Rock, at 3.56pm. They landed at 4.18pm on a property about 20 metres from the scene where NSW Ambulance paramedics were providing initial care on the roadside.

The rider, believed to be about 21, had suffered a serious isolated head injury.  The CareFlight medical team placed him in an induced coma, intubating and ventilating him.

He was then transferred to the waiting helicopter for the flight to Westmead Hospital.

Police were on the scene and will investigate the cause of the crash.