A panicked and bleeding swimmer rescued off rocks last week highlights the dangers of a "changing beach".

Entrepreneur James Madelin alerted emergency services to Auckland's west coast after a child asked for his help at Karekare Beach on Tuesday about 4pm.

He said the boy, aged about 10, told him his dad was stuck on a rock.

The boy's father, believed to be in his 40s, had crawled on to the Wedding Cake Rock - named because it has a slice missing - and looked pale, exhausted and in a state of shock after being bashed about by unexpected swells.


"He had scrambled on to the rocks in haste, mid-panic and with very little energy left so his legs were cut up a bit," Madelin said.

Surfer and local resident Clint Bishop jumped into the water and tried to encourage him off the rock.

"I just put my jumper on him and tried to get him to jump off the rock. It took about 15 minutes to coax him to jump," Bishop said.

Karekare Surf Life Saving media spokesman Matt Wade said they feared a tragedy because of changes in the beach's sand movement.

"There is a massive dump of sand slowly moving northwards. We are starting to see the impact because, at full tide, you can now get to rocks that used to be inaccessible," Wade said.

"But that means there are rock points which are completely out of sight. If the tide comes in and the swell comes up, the rocks are completely smashed.

"We are worried someone will go out there mid-week and the swell will come up and then there will be a tragedy."

He said swimmers and rock fishermen needed to be more aware of tidal patterns, changing conditions and "watching their escape path".