While flights across the US have been cancelled due to the deep freeze of the polar vortex, flights in Bremen, Germany were cancelled for an entirely different reason: a UFO.

On Monday night, an unidentified flying object showed up on Bremen Airport’s radar several times over three hours from 6.30pm to 9.30pm, causing one flight to be cancelled, one diverted and other delayed as police and airport officials investigated the UFO activity.

According to the Local.DE, Bremen police were alerted to potential UFO activity when a patrol car apparently saw the object around 6:30 p.m. Witnesses report that “It looked like a plane. It had lights but was a lot louder.”

A spokesman for German Air Traffic Control told the Weser Kurier: “It had normal lights, red and green and an approach light on both ... adding that whatever the UFO was, it could be seen through binoculars from the airport’s traffic control tower.

A police helicopter was sent off in pursuit, but was unable to track down the UFO. A Bremen police spokesman told the Local,“We still don’t know what it was, but it was there.” The hunt for the UFO is still on as officers investigate the case on grounds of unauthorized intrusion into controlled air space. Possible explanations include that it was a drone, a balloon-like aircraft or aliens attempting to turn Earth into a breeding colony.

• Bremen UFO 'looked like a plane but was louder'