Authorities are trying to find out who made a threat that forced a New York City-bound Air China flight to turn around and return to Beijing in the middle of the trip.

Information about the threat, the nature of which is still unclear, was provided by the US, but "it could have been forged and released from inside the country", a Beijing airport police spokesman told China Daily on condition of anonymity.

Officials are making efforts to track down who sent the false threat, he said.