The person pulled from the water was a man in his 60s, said the helicopter service.
Henderson resident Nigel Heard said he and a family member arrived at the beach about 4.45pm on Tuesday and saw a guard running from the surf lifesaving club to the beach.
He described conditions at the beach as awful and "pretty wild".
As Heard walked towards what is known as "the cut" he noticed more lifeguards running up the dunes.
"They were really racing to get there," he said.
As they got closer towards the south end of the beach, he saw lifeguards and paramedics giving CPR to a swimmer.
"As we got closer, we could see someone on the ground," said Heard.
"They were going for it. It was very intense.
"There was a lifeguard or ambulance staff member working on him, giving him CPR. They were really going for it.
"They just had this look about them that they were focused on what they were doing and nothing else around them mattered.
He said CPR was performed for at least 30 minutes with both the lifeguards and paramedics working in tandem to help the man.
"It was as if they were 'one'. There didn't seem to be any differentiation between the paramedics and the lifesavers. It was more everyone mucking in and doing their best.
"They didn't give up, they really, really tried. I was impressed with the effort."
After a spell around the rocks, away from the scene, he made his way back.
By this stage other emergency services including fire, the rescue helicopter and police had arrived.
He praised the efforts of the emergency services at the beach.
"Just the earnestness of the rescue services really impressed me, and the professionalism of them. I thought how lucky we are they are there and the fact that they didn't give up."
Police said while medical assistance was provided at the scene unfortunately the person died.
The man's death has been referred to the Coroner.
According to Water Safety NZ there have been seven drownings this year.
The statistics do not include a teenage swimmer who was discovered in a home pool at a Christchurch property on Sunday.
Last year 69 people drowned.