A Bell 206 helicopter has crashed in bushland in Sydney's north killing 2 occupants.

The incident which happened at approximately 0900 AEST occurred during bad weather with the wreckage strewn over a large area over difficult terrain.

The wreckage was found about 100 metres into the bush, at the bottom of a 10-15m cliff face that emergency services workers could only reach on foot and by abseiling down. 

Parts of the helicopter had been on fire when crews got to it with reports of a strong smell of fuel in the area. Police have not ruled out finding more bodies as the search continues.