A rising supply of "flexi-room" apartments has drawn a warning from authorities - people who use the undersized areas as bedrooms could be fined.
Auckland Council sets minimum sizes for one, two and three-bedroom apartments and those not meeting the standards are being sold as "flexi-room" residences.
Some "two-room flexi" apartments are being sold for more than $600,000.
But apartment-dwellers who move a bed into a "flexi" room could be hit with a $750 fine under council rules capping the number of bedrooms permitted in the tiny units. The rules came into force in 2009 but are under fresh scrutiny as high-rises crop up around the city.
A phenomenon that began in big cities such as New York, flexi-rooms are included on plans as spaces for a study, media room or storage area. But many buyers intend to use them as bedrooms.
Auckland Council's District Plan has the minimum size for a three-bedroom Central Auckland apartment as 90sq m; two bedrooms as 70sq m; and one bedroom as 45sq m.
Council resource consent manager David Oakhill said flexi-rooms used as bedrooms would breach the District Plan and possibly contravene resource consents.
Although no breaches had come to the council's attention yet, owners could be liable for a $750 fine or even court action, he said.
Ray White real estate agent Susan Rogers-Allan, who is selling apartments in the Freemans Bay Urba Residences, said some potential buyers had indicated they would use the flexi-rooms as bedrooms.
They were just a little smaller than bedrooms but often had wardrobes and plenty of space for a bed, she said. "We tell them exactly what it is so they know what they're buying."
Rogers-Allan lives in a two-bedroom city apartment that is smaller than the 70sq m limit, but because it was built before the rules came into force, she wouldn't have to sell it as a "two-room flexi".
"It's a fine size for a two-bedroom apartment and some of the Urba developments [which must advise if spaces contain flexi-rooms] are bigger than this," she said.
Barfoot & Thompson agent Alastair Brown, who sells Queen's Residences apartments in the city, said buyers had told them they wanted to use the flexi-room as an extra bedroom.
Real Estate Institute chief executive Helen O'Sullivan said the issue could prove problematic. "Purchasers need to be very aware of the distinction between a bedroom and a flexi-room, particularly if they're buying for investment."