Thousands of secret reports on New Zealand UFO sightings have been released, detailing mysterious unexplained sightings from the public and military personnel.

Read New Zealand"s UFO files here

The files include every witness account of unidentified flying objects reported to authorities since early 1952, including the infamous 1978 Kaikoura mystery.

Detailed in more than 2000 pages of files are letters from people who claim to be in touch with alien beings, sketches from witnesses and media reports.

Some of the earliest reports come from the president of the Civilian Saucer Investigation (New Zealand) group, Harold H. Fulton, thanking a witness who wrote to him about a sighting.

The witness had seen a "strange, bowl-shaped object that he saw fall from a clear sky".

"As the object fell it made a hissing sound, hit the wharf pier he was standing on and then bounced high and landed on a Government survey vessel," the letter said.

The files had been held by Archives New Zealand, which was to make them available in February after requests from the public, but the Defence Force stepped in saying it needed to remove personal identification to comply with the Privacy Act.

Access to the original files will be restricted until the year 2050 at the earliest for personal privacy reasons.

Before their release, Squadron Leader Kavae Tamariki said the Defence Force would not comment on the files" content.

"We"ve just been a collection point for the information. We don"t investigate or make reports, we haven"t substantiated anything in them."

The Defence Force did not have the resources to investigate UFO sightings, Tamariki said.

The director of research group UFOCUS NZ, Suzanne Hansen, said she had been trying to get hold of the files for nearly two years.

"I started lobbying, and at first they said there was no way in the foreseeable future they"d be released. It"s been a long time coming."

Hansen said she hoped the files would reveal more detail about some of New Zealand"s most famous cases, including the Kaikoura sighting on December 21, 1978.

Wellington man John Cordy, 77, was in the air traffic control tower on that night and still maintains there was no logical explanation for what happened.

He and his colleague witnessed inexplicable radar readings at a time when no aircraft were cleared to be in the area.