An investigation has been launched into how two Auckland homes were sold five times in four days as the practice of “flipping” continues to boom in New Zealand’s largest city and hottest property market.

The two houses are located side by side in the suburb of Mangere Bridge in south Auckland, where flipping is most common, according to an analyst from CoreLogic.

Flipping is loosely defined as properties which are sold twice or more within a single year, and properties sold twice or more within the space of six months raise particular concerns for regulators.

Last year, 1,831 Auckland properties changed hands twice or more within a single year, and 74 within a single month, according to CoreLogic.

One of the properties, a sprawling Victorian homestead, was sold for NZ$1.45m (US$1m) in February of last year, sold again on 4 August for NZ$2.4m and bought four days later by property investor Treasure Plus for NZ$2.8m.

Within a six month period the value of the property nearly doubled, making it a classic example of flipping.

A modest family home next to the historic villa was sold three times in the same week of August, eventually falling into the hands of the same developer who bought the homestead next door, Treasure Plus.

On 4 August the humble bungalow sold for NZ$1.9m dollars – four days later its value had risen by NZ$150,000 when it was bought by Treasure Plus for NZ$2.05m dollars.

The New Zealand Herald reported the developer had no knowledge of the prior transactions on the properties and planned to demolish both homes and build 18 townhouses.

Kevin Lampen-Smith, chief executive of the Real Estate Agents Authority, said his agency would investigate both transactions because the speed of how quickly they changed hands had raised red flags. He was also concerned that flipping had been on the rise in Auckland, where the average house price has reached NZ$1m.

“The natural question is if the property has been bought and sold a couple of times and the price keeps on going up, was the initial vendor looked after?,” said Lampen-Smith.

“Any time transactions take place very quickly you have increased concern to make sure all parties are fully informed of the decisions they are making.”

Nick Goodall, a senior research analyst for CoreLogic, said while contemporaneous transactions were not illegal there were ethical concerns if unscrupulous developers took advantage of less-educated vendors.

Goodall said 7.4% of Auckland property transactions were identified as potential “flips” in 2016, with high net migration and a shortage of housing pushing up prices.

The cities of Hamilton and Tauranga, both within a two-hour drive from Auckland, had also been identified as flipping hot-spots, with 6.4% of sales in Hamilton held for less than one year, and 4.9% in Tauranga.

“Flipping can mean buying a property and doing it up to sell it on, or buying a property, holding onto it, and then selling it on.” said Goodall.

“I am not sure if you can call it deception but there are definitely cases where someone who is educated on the market can take advantage of someone who is not. And that situation could well be one of those.”

Auckland Council said they would also investigate the heritage value of the homestead sold for NZ$2.8m, as it may be of historical significance and to be demolished for redevelopment would need archeological approval from Heritage New Zealand.