THE start of winter will bring powerful swell to the North Coast this weekend.

Rock fisherman, boat users, surfers and swimmers are all urged to be vigilant after the Bureau of Meteorology issued a hazardous surf warning.

A warning has been issued for the entire NSW coastline with powerful conditions forecast to last until at least late Saturday.

Southern-facing beaches and exposed rock platforms are expected to bear the brunt of the conditions, with swell in excess of four metres predicted in some areas.

With waves and wind stronger offshore, boat users are being urged to be particularly mindful of the conditions throughout the weekend, and exercise extreme caution if crossing river bars.

The onset of winter is traditionally a great time for rock fishing, but fisherman are urged to wear the correct safety gear including a lifejacket, as well as fish with a friend, take care when getting on and off rock platforms, and to never turn their back on the ocean.

It is anticipated that the swell conditions will begin to ease by Sunday, though caution is still advised as the forecast is continually revised.

"While the strong winds and large waves are likely to deter many people from entering the over the next couple of day, it is important that beachgoers are still mindful of the conditions,” Surf Life Saving NSW duty operations coordinator Andrew Ugarte said.

Mr Ugarte urged the public to take the warnings seriously, particularly because volunteer patrols have finished for the season, and only a few beaches across the state are currently manned by lifeguards.

"Please take note of the safety warnings and if you have any doubt whatsoever about your ability to handle the water it's better not to go in,” Mr Ugarte said.

General safety tips during hazardous surf conditions:

• Avoid rock fishing and water activities on exposed beaches or rock-shelves
• Only swim at patrolled beaches between the red and yellow flags. See www.beachsafe.org.au for patrolled locations and times
• Check the official Bureau of Meteorology (BOM) forecast before undertaking rock fishing and water activities
• Boat users should seek advice from Marine Rescue NSW and always wear a lifejacket
• If you witness an in-water emergency, dial Triple Zero Police.