Çat Valley in Nevşehir. The underground city dates from 3000BCE, but who built it and why remains a mystery Jean & Nathalie

A massive underground city that dates back 5,000 years has been discovered in Turkey's Central Anatolian province.

The city, unearthed by archaeologists, is believed to be the world's biggest underground city ever to be found.

According to Turkey's Hurriyet Daily News, the researchers unearthed tunnels and passages during work on an urban transformation project.

Around 1,500 buildings in the area were destroyed to make way for new homes. While moving earth to begin construction, the giant city was discovered.

Mehmet Ergün Turan, head of Turkey's Housing Development Administration's (TOKİ), said the area was immediately announced as an area of preservation: "It is not a known underground city. 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."

This 5,000 year-old city joins an extensive network of underground dwellings in the area. The largest, Kaymakli, is still used today for storage. Another, underneath the town of Derinkuyu, is the deepest of subterranean cities, being 11 stories below ground and home to an estimated 20,000 people

The latest city is located around Nevşehir. It contains escape galleries and hidden churches. Other underground cities discovered do not come close to meeting the size of the latest find, Nevşehir mayor Hasan Ünver said.

"The underground city was discovered when we began the destruction in line with the protocol. The first galleries were spotted in 2013. We applied to the [Cultural and Natural Heritage] Preservation Board and the area was officially registered," Ünver said, adding artefacts have already been excavated from the site.

Archaeologists hope to find out more about the city, including who created it and how many people lived there, over the coming years.