Turkish housing developers accidentally discovered an ancient underground city in what could be the biggest archaeological find of 2014, the Hurriyet Daily News reported.

Little is known about the 5,000-year-old underground city discovered Dec. 28 in the province of Nevşehir, located in Turkey's Central Anatolian region.

The country's Housing Development Administration, TOKİ, discovered the underground series of buildings, galleries and churches while clearing the land around the Nevşehir fortress for a new residential project. Officials don't even know what it was called yet.

"It is not a known underground city," Mehmet Ergün Turan, head of TOKİ, told the Hurriyet Daily News. "Tunnel passages of seven kilometers are being discussed.

"We stopped the construction we were planning to do on these areas when an underground city was discovered."

The area is now registered with the Cultural and Natural Heritage Preservation Board and an archaeological investigation is expected, the newspaper reported.

Though the agency already paid 90 million Turkish Liras ($38 million) for the project, Turan said it's not a loss because the underground city may be the largest one in the world.

Housing officials are moving the urban project to a location just outside the city.