A NSW Fire Brigade spokesperson said the fire had burnt out an area 100m by 80m, but was not threatening any property.

The fire started at 3.50pm, and NSW Fire Brigade crews from Bulli, Thirroul, Unanderra and Rural Fire Service volunteers were at the scene.

"It's an area of bush and they're having a bit of difficulty with water availability," the spokesman said.

"One side of it is along the beach, there are no hydrants along there but we have got water tankers on scene.

"The fire is contained, there is no property in danger. It's going to burn itself out and create a bit of smoke for a little while."