Fire crews are fighting to protect properties in northern Sydney as a fire continues to burn in Ku-ring-gai Chase National Park.

The fire broke out on Friday night with crews working to protect properties at Lovett, Morning and Elvina Bays, the RFS said.

Some remote properties could be hit with smoke and burning embers, while smoky conditions were hitting Terrey Hills and areas of the northern beaches.

A helicopter is assisting crews to contain the fire, which is one of 95 fires burning across the state.