Files documenting more than 1600 UFO sightings over the last 50 years have been released as France's National Center for Space Studies opens its X-Files to the public. The site's server crashed under the load after just three hours as the world's UFO spotters descended on the archive in search of answers.

In what is believed to be a world first, more than 100,000 pages of witness testimony, photographs, film and audio recordings have been published at www.cnes-geipan.fr. Dating back to 1954, the archive will continue to be updated as new cases are reported, says Jacques Patenet - head of the space agency's UFO investigative team.

Fifty to 100 sightings are reported every year, with Patenet's team investigating around 10 per cent. Almost a quarter of reports are classified as "Type D", meaning "despite good or very good data and credible witnesses, we are confronted with something we can`t explain," he said.

Security guards stood watch outside the space agency headquarters as the announcement was made, "to screen out uninvited ufologists."