Two UFOs (Unidentified flying objects) racing across the sky at an estimated 4,000km/h have been captured by a film crew working near Queenstown, New Zealand.

The Colour in your Life film crew were shooting some footage of a motorbike riding across a bridge but when they came to look at the footage, they noticed two objects racing across the sky in the background.

After slowing down the footage, they saw how the two objects appeared from some nearby trees and speed off into the sky in an upwards trajectory.

"I just happened to stop the footage right when these objects appeared," producer Graeme Stevenson wrote on YouTube. "At the speed they seem to be travelling, we worked out about 4,000 kilometres an hour, they were about a half a K away when they came out of the forest.

"This was the first week in April on the South Island of New Zealand and the same shaped objects were filmed in the Netherlands the same week. Weird or what? No air bases down there and I don't think ducks and insects or anything else I know of fly at that speed."

Colour in your Life production manager Tanita Cree told MailOnline: "We were all like, what was that? It was the speed they were moving at, they just jumped out of the trees."

Another member of the team noted that the objects were unlikely to be birds as no animal can accelerate to such a fast speed in such a short space of time.

Other viewers are less convinced, however, suggesting the footage was a publicity stunt by the film crew: "Great publicity stunt for your TV show, look, it worked, almost 13,000 views," one wrote, while another added with a hint of sarcasm: "A good marketing strategy?"