David Chung said it was "lucky no one got pulled into the ocean" when a wave smashed into Redhead Beach Surf Lifesaving Club, threatening the safety of people and raising questions about the long-term future of the building.
Some say it was the biggest swell ever seen at Redhead in their lifetimes.
Mr Chung, of Redhead, took photos of the wave hitting the club at about 9am on Saturday.
He said it was an hour before the peak of the high tide, so the wave "caught everyone off guard".
"When the surge came there was so much volume of water hitting the club house," he said.
"People with their children and dogs ended up trapped under the stairs."
He said the force of the wave "pushed someone into the glass door of the lifeguard's room with so much force it smashed the glass door".
"All the long-term locals, some who have lived here for over 50 years, were saying yesterday [Saturday] was the biggest swell they've seen.
"The seas have uncovered rocks that haven't been seen for decades and a lot of sand has been taken off the beach."
Hunter Surf Life Saving president Henry Scruton said the Redhead club had "an enormous rock escarpment built underneath it" when the club was established.
"Tonnes of rock were put underneath the club specifically to assist the club house when there is a big sea. It has done an exceptional job," Mr Scruton said.
"What they copped on Saturday was above and beyond what anybody had ever seen before. It was something completely abnormal."
Mr Scruton said the wave "only went into the coffee shop".
"They did get some water inside, but no major damage," he said.
Redhead locals told him it was the "biggest swell to come to the area".
Mr Scruton said surf clubs were assessing the future of their buildings due to the threats of erosion and rising seas.
"Waves have got into the storage area of Cooks Hill Surf Club's older premises on several occasions [at Bar Beach]," Mr Scruton said.
"The water gets in, does damage and deposits lots of sand. Their new section to the north seems a lot more weatherproof. The older club on the southern side does cop quite a battering occasionally."
Mr Scruton said surf clubs were in "continual conversations with Newcastle City Council".
"The Dixon Park club is sitting quite happily on top of the hill. Merewether is trying to get a lease to rebuild a bit further back, higher up and away from the big seas when they come."
Video posted online on Saturday also showed people's beachfront backyards being eroded at North Entrance on the Central Coast.
Academics say sea level rise is playing a part in the erosion of beaches.
University of Newcastle Associate Professor Iftekhar Ahmed, a climate change adaptation expert, told the Newcastle Herald last month that "the sea level is rising".
"It's an inescapable fact. The icebergs are melting," A/Prof Ahmed said.
Heavy seas caused the worst erosion ever seen on a long stretch of beach on the northern Central Coast, covering Budgewoi and Lakes beaches in early March. The dunes were eaten away, with millions of tonnes of sand eroded.
With the rising seas and stormy weather, currents and waves also rise.
"There's also a scouring action of water under the soil and salinity intrusion. So the saline water starts going inland. It infiltrates and bloats it, weakening the soil structure from underneath," A/Prof Ahmed said.
"It's a slow process. It's been happening for quite a long time now. This has already weakened the soil. So if there's impact by waves, it crumbles and falls off."
He believes the "long-term solution is to retreat", although dykes are also an option.
