Recently released United States Air Force files have confirmed that a suspected UFO photographed in the skies above Auckland more than 60 years ago was actually just a cloud.
The Project Blue Book files, which have recently been made available online, related to USAF investigations from 1947-1969.
One of the images shows a circular disc shape in the sky, which thecid.com UFO website reported as being above Auckland in mid-1951.
This image was titled "Winter 1951'.
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The photographer believed it to be a flying saucer, but the USAF concluded that it was in fact a lenticular cloud, the Daily Mail reported.
The lens-shaped formations were the result of moist air that has condensed at a high altitude.
The clouds were formed when the air temperature dropped and moisture droplets were pushed up a steep slope by high winds, the paper said.
Another famous image was of the Lubbock Lights, which was reported in Texas in 1951, that were likely to be plover birds, which had white breasts that reflected light from cities below.
The Project Blue Book investigated more than 12,000 suspected UFO encounters. More than 700 cases remain unsolved, accounting for 5.5 per cent of the files.
See the images here