Linguists say they have discovered a new and unique language, called Koro, in north-eastern India, but they warn that it is highly endangered.

Only about 800 people are believed to speak the Tibeto-Burman language, and few of them are under the age of 20, according to the researchers who discovered Koro during an expedition as part of National Geographic's Enduring Voices project.

The language, they said, has never been written down.