A police spokesperson said this morning the person died in Christchurch Hospital after being rescued by the Sumner Lifeboat crew about 6.30pm on Tuesday.
An eyewitness said last night the person had received CPR after the rescue.
The person was initially transported to the Sumner Lifeboat Station, a St John spokesperson said.
Ambulance crews then took the person to Christchurch Hospital in a critical condition.
The death will be referred to the Coroner, police said.