NSW firefighters say the weather is now on their side, a day after heat and strong winds fuelled a major bushfire at a popular beachside tourist spot north of Sydney.

Rural Fire Service spokesman Brendan Doyle says firefighters will take advantage of lower temperatures to control the blaze.

"Today and tomorrow, the weather is definitely on our side," he told AAP on Sunday.

"We'll be using it to deepen containment lines."

The cool change came after the Rural Fire Service issued an emergency alert on Saturday for Barrenjoey Headland, near Palm Beach.

Visitors to the headland were warned to shelter near its historic lighthouse after an access trail was cut off but no one was injured and the blaze has since been downgraded to an advice level.

The fire burned through 17 hectares of bushland on Saturday and overnight around the headland which is adjacent to Palm Beach - an area known as "Summer Bay" in the long-running television soapie Home and Away.

About 30 firefighters are expected to monitor the situation over the rest of the weekend to control the blaze and attend to hotspots.

"We're allowing that fire to slowly burn down to the water line," Mr Doyle said.

He says aerial images will help crews monitor progress.

RFS firefighters managed to save the iconic lighthouse but the flames did reach a nearby cottage.

Mr Doyle said a building impact assessment team would be at the site later on Sunday to gauge the extent of damage to the structure's roof.