Massive waves were slamming into the NSW coast on Tuesday as a deep low pressure system churns up the Tasman Sea.

Image: Avoca Beach on Tuesday. Credit: Thom Newman.

Maximum wave heights reached 9.8 metres near Batemans Bay on Tuesday morning as a large southerly swell hit the south coast of NSW.

The peak of this swell then made its way up to Sydney, where maximum wave heights were reaching a whopping 11.9 metres at midday. This is on par with the 12 metre peak waves that were recorded near Sydney during the June 2016 East Coast Low swell, which was an event that caused widespread coastal erosion.

Image: A maximum wave height of 11.9 metres was registered off the coast of Sydney at midday on Tuesday. Credit: Manly Hydraulics Laboratory. 

Fortunately, today's southerly swell is not causing as much coastal erosion as the easterly swell did in June 2016. Sydney's beaches are more exposed to the east and get some protection from big southerly swells.

Despite being shielded from some of the biggest waves today, Sydney's beaches are still being hit by huge sets. Beaches are unsafe and should be avoided. Even venturing down to the shoreline or rock shelves to have a look at the surf could be life-threatening.

The large swell will continue to spread along the state's north coast during the next 12-24 hours, before gradually easing through the middle of the week.