The Bureau of Meteorology has issued a hazardous surf warning for almost the entirety of the NSW coast, from Eden to Byron.

Conditions are expected to be hazardous for coastal activities such as rock fishing, boating and swimming.

Surf Life Saving Lower North Coast Branch president Brian Wilcox said duty officers and first responders in the area were prepared.

"We pretty much put everyone on alert," he said.

"Once they're notified they're ready to go."

Mr Wilcox said while the forecast swell was exceptionally big, how much effect it had on inshore conditions would depend on the swell direction.

"If it's coming from the straight south then it tends to go straight past," he said.

"As soon as it gets some east in it is when it gets really big."

At present the swell is predicted to come from the straight south, with gale force south-westerly winds set to accompany it.

Australian surf forecast website Swellnet is predicting waves of up to 15-20 feet - or six times overhead - on southern-facing beaches around the Great Lakes by tomorrow afternoon.

Non-southern-facing beaches are expected to have waves of around eight feet, or three times overhead.

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Mr Wilcox said while swimmers were less likely to get into trouble at this time of year, rock fishermen remained a concern.

A man and a woman had to be rescued in June after being swept off rocks while fishing at Pacific Palms.

Mr Wilcox said the dangerous surf conditions were not only a concern for those having to be rescued, but also for the responders.

"It's a concern for us because if anything happens we have to go out in it," he said.

"It can be quite harrowing."

He hoped for this reason people would make sensible decisions around the water during the upcoming swell.

He was less concerned about surfers, saying conditions would be too big for any novices to tackle and praising experienced surfers for often being the first to respond in rescue situations.

The large seas are being caused by an intense low pressure system over the southern part of the Tasman Sea.

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