An offer, thought to be about $7.5 million, has been made to purchase a private island just off the Coromandel Coast near Paunui.

But media reports suggest the sale of Slipper Island, one of a handful of privately owned islands in New Zealand, has caused a split within the Needham family who have owned it for 45 years.

Slipper Island. Image: Google Earth

Fairfax reports a Remuera-based property developer signed an agreement for sale and purchase, with the parties now going through the due diligence process which will take about one month.

It is believed an offer of $7.5m was made for the purchase of Slipper Island.

Speaking to SunLive New Zealand Sotherby's International Realty agent Brian Brakenridge confirms a conditional sales and purchase agreement was signed in the past fortnight.

But he would not confirm the name of the Remuera-based developer or the reported $7.5m offer as he is constrained by confidentiality to the vendor.

'As a real estate agent I am bound by that confidentiality, it's no different from any other commercial transaction.

'I've been forbidden to discuss any details whatsoever, it's company policy but we'd also simply be totally unprofessional to comment on any details around any silent purchase agreement.”

He also declined to comment whether other offers had been made for the island.

SunLive has attempted to contact Slipper Island Resort Ltd majority shareholder Elizabeth Needham for comment has not receive a reply.