The Real Estate Agents Authority is investigating the sale of two neighbouring Auckland properties that changed hands a total of five times in four days.

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One changed hands three times in four days, while its neighbouring property was sold twice in that time.

The two houses on Coronation Rd, Mangere, were sold on the same day last August by Sha Liu to property developer Treasure Plus for nearly $5 million.

The vendor, who had bought them from two different owners four days earlier, made a profit of more than $500,000.

Real Estate Agents Authority chief executive Kevin Lampen-Smith said it was looking into how the real estate agents handled the deals.

"A bit of property speculation is not really the purview of the Real Estate Agents Authority and there is nothing legally wrong with contemporaneous sales, but it does increase the risk in the transaction and the real estate agents [need to be] very careful to manage their legal obligations."

Nick Goodall of the property research firm CoreLogic said all together the two houses were sold a total of five times in that period. He said in one of the transactions one of the properties, a bungalow, changed hands twice in a day.

"There's been a contemporaneous sale on both occasions, which means that it sold twice but both settled on the same day so the person that owned it in the interim never actually owned it for more than a minute effectively," he said.

"Those people who owned it in the interim saw the development potential bought it on the premise and then looked for a buyer, or had a buyer ready for it and then agreed the sale to settle on the same day."

It was not illegal to sell a property after owning it for just one minute, Mr Goodall said.

"I think there's some level of disclosure that should occur and I'm not sure what's happened on this occasion but certainly you can buy a property and settle on the same day as you were due to settle your own purchase of it," he said.

The sale price on the other property, an old homestead, nearly doubled in six months. Mr Goodall said investors saw the development potential of properties under Auckland's development blueprint, the Unitary Plan, where in some cases 10 dwellings could be built on land that currently had one house.

An Auckland Council spokeswoman said under the Unitary Plan, which is largely in place, the house was not a scheduled heritage building and demolition was a permitted activity.

However, the council is currently undertaking a Mangere Bridge Heritage Survey and staff had recently visited the site to undertake an initial heritage assessment.

It appeared that people had lived there prior to 1900 and Heritage New Zealand approval would probably be needed before earthworks went ahead, she said.

There were no resource consent applications lodged for either of the properties, she said.