Boaties have been told to destroy life jackets over ten years old which are likely to fail.
Maritime New Zealand has found a number of lifejackets made in the 1980s no longer comply with New Zealand safety standards.
Its general manager maritime compliance, Kenny Crawford, said the lifejackets were likely to fail if used and should be destroyed so they cannot be reused or on-sold.
These type of life jackets have a cotton-like fluff filling that loses buoyancy over time so if the jacket gets wet it will absorb water and pull the wearer down.
When tested overseas, the old lifejackets sank within ten minutes, Mr Crawford said.
"They will have deteriorated over the years and then there's a risk there that you put them on when you need them in an emergency, you go into the water and they don't do what they're supposed to do," he said.
"You should not be putting any faith in these old life jackets.
"You might think they'll save your life but there is a high possibility they will not save your life."
Mr Crawford said these old lifejackets complied with international rules when they were manufactured, and many of them have the old standards "S" logo on them. However, they no longer comply with the modern New Zealand standard for lifejackets.
The old life jackets also have cotton straps that rot over time and could cause the safety device to come off the wearer.
Mr Crawford said it was not known how many of the old lifejackets were being used.
"Lifejackets are being sold second-hand, handed down to families.
"You'd think ... they would upgrade their life jackets every few years or so but this doesn't appear to be happening," he said.
TradeMe has removed several listings of these old lifejackets on the advice of Maritime New Zealand.