A mysterious object seen in skies over the Tasman Sea near Kaitaia is baffling UFO experts.

Last month, The Northern News reported that UFO Focus New Zealand (UFOCUS NZ) and world UFO expert Dr Bruce Maccabee were studying a series of unusual photographs taken at Ahipara on April 28.

The digital photos, taken of the sky and sea at 5.42pm, showed a bright object which did not look like a cloud and had the appearance of a craft.

The story attracted intense interest and remained one of the most viewed stories on the Northland page of the Stuff news website three weeks after publication.

Last week, UFOCUS released its report on the sighting and we can now bring you photos.

The report says the photographer watched the object for nearly five minutes while it moved silently across the sky in a northerly direction reducing in size and disappearing.

Dr Maccabee, an optical physicist in the United States Navy, says in the report that the object does not display flight characteristics that distinguish it as a 'craft' of unknown origin.

However, its shape suggests a circular 'something' with a dome-like top.

The object could also be a jet aircraft's vapour trail viewed end on, he says.

Air Traffic Control says there were no scheduled flights in the area at the time.

It would expect to see consistency of shape from both trails and a 'flow-off' similar to a cirrus cloud blown by winds if the object was a jet contrail.

Instead, the shapes in the photos are compact.

UFOCUS has consulted the Carter Observatory and ruled out the object being space junk or a meteorite, says the group's coordinator Suzy Hansen.

"Neither space junk nor a meteorite would present the images we have. They would be a ball of fire burning up rather than a bright object."

Dr Maccabee has not commented on whether the photographer may have manipulated the eight photos, says Ms Hansen.

While the UFO group cannot rule out the possibility of manipulation, she thinks it is unlikely the photos are a hoax.

"I have directly asked the witness if he hoaxed the photos, and he was most adamant that he had not.

"When you see the full series, you will see that it would take hours and hours to hoax such a thing."

UFOCUS and Dr Maccabee have agreed that no firm conclusion can be drawn about what the object is, says Ms Hansen.

They are classifying it as an unusual aerial phenomenon - UAP - but are keen to know what the public thinks it may be.